Multidisciplinary studies have led to the discovery and characterization of cysteine string proteins (csps) in both Drosophila and Torpedo. Phenotypic analysis of csp mutants in Drosophila demonstrates a crucial role for csp in synaptic transmission. Expression studies of Torpedo csp (Tcsp) in Xenopus oocytes suggests that the protein has some role in the function of presynaptic Ca2+ channels. However, biochemical purification of Tcsp indicates that is associated with synaptic vesicles rather than with the plasma membrane of presynaptic terminals where (...) Ca2+ channels reside. These results suggest a model in which csps serve as a link by which docked synaptic vesicles could modulate the activity of presynaptic Ca2+ channels. (shrink)

D‐amino acids are being recognized as functionally important molecules in mammals. We recently identified endogenous D‐cysteine in mammalian brain. D‐cysteine is present in neonatal brain in substantial amounts (mM) and decreases with postnatal development. D‐cysteine binds to MARCKS and a host of proteins implicated in cell division and neurodevelopmental disorders. D‐cysteine decreases phosphorylation of MARCKS in neural progenitor cells (NPCs) affecting its translocation. D‐cysteine controls NPC proliferation by inhibiting AKT signaling. Exogenous D‐cysteine inhibits AKT (...) phosphorylation at Thr 308 and Ser 473 in NPCs. D‐cysteine treatment of NPCs led to 50% reduction in phosphorylation of Foxo1 at Ser 256 and Foxo3a at Ser 253. We hypothesize that in the developing brain endogenous D‐cysteine is as a physiologic regulator of NPC proliferation by inhibiting AKT signaling mediated by Foxo1 and Foxo3a. Endogenous D‐cysteine may regulate mammalian neurodevelopment with roles in schizophrenia and Alzheimer's disease (AD). (shrink)

A single protein molecule with one or more cysteine residues can occupy a plurality of unique residue and oxidation‐chemotype specified proteoforms that I term oxiforms. In binary reduced or oxidised terms, one molecule with three cysteines will adopt one of eight unique oxiforms. Residue‐defined sulfur chemistry endows specific oxiforms with distinct functionally‐relevant biophysical properties (e.g., steric effects). Their emergent complexity means a functionally‐relevant effect may only manifest when multiple cysteines are oxidised. Like how mixing colours makes new shades, combining (...) discrete redox chemistries—colours—can create a kaleidoscope of oxiform hues. The sheer diversity of oxiforms co‐existing within the human body provides a biological basis for redox heterogeneity. Of evolutionary significance, oxiforms may enable individual cells to mount a broad spectrum of responses to the same stimulus. Their biological significance, however plausible, is speculative because protein‐specific oxiforms remain essentially unexplored. Excitingly, pioneering new techniques can push the field into uncharted territory by quantifying oxiforms. The oxiform concept can advance our understanding of redox‐regulation in health and disease. (shrink)

Graphical AbstractPheomelanogenesis may have evolved as an excretory mechanism to remove excess cysteine, and in humans this might potentially confer a greater ability to avoid disease such as Parkinson's and Alzheimer's disease, in which excess cysteine is a contributory cause.

Rho GTPases are critically important and are centrally positioned regulators of the actomyosin cytoskeleton. By influencing the organization and architecture of the cytoskeleton, Rho proteins play prominent roles in many cellular processes including adhesion, migration, intra‐cellular transportation, and proliferation. The most important method of Rho GTPase regulation is via the GTPase cycle; however, post‐translational modifications (PTMs) also play critical roles in Rho protein regulation. Relative to other PTMs such as lipidation or phosphorylation that have been extensively characterized, protein oxidation is (...) a regulatory PTM that has been poorly studied. Protein oxidation primarily occurs from the reaction of reactive oxygen species (ROS), such as hydrogen peroxide (H2O2), with amino acid side chain thiols on cysteine (Cys) and methionine (Met) residues. The versatile redox modifications of cysteine residues exemplify their integral role in cell signalling processes. Here we review prominent members of the Rho GTPase family and discuss how lipidation, phosphorylation, and oxidation on conserved cysteine residues affects their regulation and function. (shrink)

Recently opposing effects of cysteine protease inhibitors, the human cystatins, on neurodegeneration have been reported. Human cystatin C is a risk factor for late‐onset Alzheimer's disease (AD), whereas human stefin B (cystatin B) has no direct involvement in AD. Conflicting data show that their target protease, cathepsin B, might be anti‐amyloidogenic, helping in amyloid‐beta (Aβ) clearance or, instead, might be involved in Aβ production. Some reports claim that cystatin C binds soluble Aβ, making transgenic animals healthier, others, in contrast, (...) that deleting cystatins genes may contribute to amyloid pathology in animal models of AD. (shrink)

Ageing is associated with a decline in autophagy and elevated reactive oxygen species (ROS), which can breach the capacity of antioxidant systems. Resulting oxidative stress can cause further cellular damage, including DNA breaks and protein misfolding. This poses a challenge for longevous organisms, including humans. In this review, we hypothesise that in the course of human evolution selective autophagy receptors (SARs) acquired the ability to sense and respond to localised oxidative stress. We posit that in the vicinity of protein aggregates (...) and dysfunctional mitochondria oxidation of key cysteine residues in SARs induces their oligomerisation which initiates autophagy. The degradation of damaged cellular components thus could reduce ROS production and restore redox homeostasis. This evolutionarily acquired function of SARs may represent one of the biological adaptations that contributed to longer lifespan. Inversely, loss of this mechanism can lead to age‐related diseases associated with impaired autophagy and oxidative stress. (shrink)

Correspondence analysis of 28 proteomes selected to span the entire realm of prokaryotes revealed universal biases in the proteins’ amino acid distribution. Integral Inner Membrane Proteins always form an individual cluster, which can then be used to predict protein localisation in unknown proteomes, independently of the organism’s biotope or kingdom. Orphan proteins are consistently rich in aromatic residues. Another bias is also ubiquitous: the amino acid composition is driven by the GþC content of the first codon position. An unexpected bias (...) is driven, in many proteomes, by the AANbox of the genetic code, suggesting some functional biochemical relationship between asparagine and lysine. Less-significant biases are driven by the rare amino acids, cysteine and tryptophan. Some allow identification of species-specific functions or localisation such as surface or exported proteins. Errors in genome annotations are also revealed by correspondence analysis, making it useful for quality control and correction. (shrink)

MutL family proteins contain an N‐terminal ATPase domain (NTD), an unstructured interdomain linker, and a C‐terminal domain (CTD), which mediates constitutive dimerization between subunits and often contains an endonuclease active site. Most MutL homologs direct strand‐specific DNA mismatch repair by cleaving the error‐containing daughter DNA strand. The strand cleavage reaction is poorly understood; however, the structure of the endonuclease active site is consistent with a two‐ or three‐metal ion cleavage mechanism. A motif required for this endonuclease activity is present in (...) the unstructured linker of Mlh1 and is conserved in all eukaryotic Mlh1 proteins, except those from metamonads, which also lack the almost absolutely conserved Mlh1 C‐terminal phenylalanine‐glutamate‐arginine‐cysteine (FERC) sequence. We hypothesize that the cysteine in the FERC sequence is autoinhibitory, as it sequesters the active site. We further hypothesize that the evolutionary co‐occurrence of the conserved linker motif with the FERC sequence indicates a functional interaction, possibly by linker motif‐mediated displacement of the inhibitory cysteine. This role is consistent with available data for interactions between the linker motif with DNA and the CTDs in the vicinity of the active site. (shrink)

The growth factor progranulin (PGRN) regulates cell division, survival, and migration. PGRN is an extracellular glycoprotein bearing multiple copies of the cysteine‐rich granulin motif. With PGRN family members in plants and slime mold, it represents one of the most ancient of the extracellular regulatory proteins still extant in modern animals. PRGN has multiple biological roles. It contributes to the regulation of early embryogenesis, to adult tissue repair and inflammation. Elevated PGRN levels often occur in cancers, and PGRN immunotherapy inhibits (...) the growth of hepatic cancer xenografts in mice. Recent studies have demonstrated roles for PGRN in neurobiology. An autosomal dominant mutation in GRN, the gene for PGRN, leads to neuronal atrophy in the frontal and temporal lobes, resulting in the disease frontotemporal lobar dementia. In this review we will discuss current knowledge of the multifaceted biology of PGRN. (shrink)

Zyxin is a low abundance phosphoprotein that is localized at sites of cell‐substratum adhesion in fibroblasts. Zyxin displays the architectural features of an intracellular signal transducer. The protein exhibits an extensive proline‐rich domain, a nuclear export signal and three copies of the LIM motif, a double zinc‐finger domain found in many proteins that play central roles in regulation of cell differentiation. Zyxin interacts with α‐actinin, members of the cysteine‐rich protein (CRP) family, proteins that display Src homology 3 (SH3) domains (...) and Ena/VASP family members. Zyxin and its partners have been implicated in the spatial control of actin filament assembly as well as in pathways important for cell differentiation. Based on its repertoire of binding partners and its behavior, zyxin may serve as a scaffold for the assembly of multimeric protein machines that function in the nucleus and at sites of cell adhesion. (shrink)

In many cells, a nitric oxide (NO) synthase inducible by immunological stimuli produces a sustained flow of NO that lasts a long time. NO is a short‐lived molecule but it is a diffusibel ligand believed to be capable of reaching distal target sites. Further, several lines of evidence indicate that cysteine‐rich motifs of metal‐binding proteins, as well as redox‐sensitive metal clusters of metalloproteins, are natural sensors of bioradicals like NO. In metalloregulatory proteins, metals are often conveniently located at binding (...) sites and bound to cysteine residues. Accordingly, disruption of the metal‐thiolate polymetallic clusters should trigger significant remodelling of the protein structure involved in regulation. We can therefore postulate that the nitrosation reaction occurring at metal centres or cysteine‐rich motifs will preclude correct binding to regulatory sites. Several examples are given of metalloregulatory proteins whose metal is bound to thiols and may then become sensitive to NO. Recent observations indicate that in response to NO synthesis, iron regulatory protein, a eukaryotic bifunctional [Fe‐S] protein, switches from acting as aconitase to being an RNA‐binding regulator, and we suggest that the interplay between NO or a NO‐derived molecule and metal clusters at critical allosteric sites may be a crucial component of the cellular response to environmental stress. (shrink)

Calpain (Cp) is a calcium (Ca2+)‐dependent cysteine protease. Activation of the major isoforms of Cp, CpI and CpII, are required for a number of important cellular processes including adherence, shape change and migration. The current concept that cytoplasmic Cp locates and associates with its regulatory subunit (Rs) and substrates as well as translocates throughout the cell via random diffusion is not compatible with the spatial and temporal constraints of cellular metabolism. The novel finding that Cp and Rs function relies (...) upon tenacious hydrophobic interactions with organelle membranes offers a unifying explanation for the paradoxical and puzzling features of Cp activation and regulation such as how nM concentrations of intracellular Ca2+ can activate Cp molecules requiring μM to mM concentrations of Ca2+ for in vitro activation, and how this protease can spatially and temporally locate specific substrates and translocate throughout the cell. We hypothesize that Cp and its regulatory moieties associate with organelles to facilitate the activation of this protease resulting in the cleavage of substrates and aid in its translocation throughout the cell. BioEssays 28: 850–859, 2006. © 2006 Wiley Periodicals, Inc. (shrink)

The endoplasmic reticulum (ER) uses various mechanisms to ensure that only properly folded proteins enter the secretory pathway. For proteins that oligomerize in the ER, the proper tertiary and quaternary structures must be achieved before their release. Although some proteins fold before oligomerization, others initiate oligomerization cotranslationally. Here, we discuss these different strategies and some of the unique problems they present for the ER quality control system. One mechanism used by the ER is thiol retention. Thiol retention operates by monitoring (...) the redox state of specific cysteine residue(s) and was discovered in studies on the assembly of IgM, a complex oligomeric glycoprotein. This system is also involved in retaining other unassembled proteins in the ER. Mutations that result in uneven numbers of cysteine residues can subject yet other proteins to thiol retention, altering their oligomerization status and function. The implications of these results on the effects of thiol retention on protein function and cell fate are discussed. BioEssays 20:546–554, 1998. © 1998 John Wiley & Sons Inc. (shrink)

The gut protozoan parasite, Giardia duodenalis, is the best characterized example of the most ancient eukaryotes, which are anaerobic and appear to be primitively amitochondrial. Apart from its obvious medical importance, Giardia is fascinating in its own right. Its prokaryotic-like anaerobic metabolism renders it selectively sensitive to some bacterial drugs, especially the nitroimidazoles, which are activated to form toxic radicals. Other features, including an enzyme that reduces oxygen directly to water, cysteine as the keeper of redox balance, a plasmid, (...) and toxin-like genes are also distinctly prokaryotic-like. But, unlike prokaryotes, Giardia has a sophisticated, highly developed cytoskeleton, bounded nuclei, linear chromosomes capped with telomeric repeats, and telomere positional regulation of gene expression. BioEssays 20:256–263, 1998.© 1998 John Wiley & Sons, Inc. (shrink)

In vertebrates, members of the cysteine‐rich protein (CRP) family are characterized by the presence of two LIM domains linked to short glycine‐rich repeats. These proteins mediate protein–protein interactions and are of fundamental importance for cell differentiation, cytoskeletal remodeling, and transcriptional regulation. To date, a vast amount of information about vertebrate CRPs has become available, including their biological functions, interacting partners, and three‐dimensional structures. Compatible with a molecular adapter role, structural data reveal that the LIM domains within these proteins represent (...) completely independent folded units bridged by flexible linker regions. The physiological roles for individual CRPs was determined by targeted gene disruption analysis and by identification of common and specific binding partners by means of yeast and mammalian two‐hybrid screens. Several CRP‐like LIM domain proteins with close structural and sequence similarity were identified in arthropods, protozoas and plants, supporting the notion that this subset of LIM domain proteins has been highly conserved over the span of evolution thereby emphasizing the importance of their function. BioEssays 25:152–162, 2003. © 2003 Wiley Periodicals, Inc. (shrink)

The Earth agglomerates and heats. Convection cells within the planetary interior expedite the cooling process. Volcanoes evolve steam, carbon dioxide, sulfur dioxide and pyrophosphate. An acidulous Hadean ocean condenses from the carbon dioxide atmosphere. Dusts and stratospheric sulfurous smogs absorb a proportion of the Sun’s rays. The cooled ocean leaks into the stressed crust and also convects. High temperature acid springs, coupled to magmatic plumes and spreading centers, emit iron, manganese, zinc, cobalt and nickel ions to the ocean. Away from (...) the spreading centers cooler alkaline spring waters emanate from the ocean floor. These bear hydrogen, formate, ammonia, hydrosulfide and minor methane thiol. The thermal potential begins to be dissipated but the chemical potential is dammed. The exhaling alkaline solutions are frustrated in their further attempt to mix thoroughly with their oceanic source by the spontaneous precipitation of biomorphic barriers of colloidal iron compounds and other minerals. It is here we surmise that organic molecules are synthesized, filtered, concentrated and adsorbed, while acetate and methane—separate products of the precursor to the reductive acetyl-coenzyme-A pathway—are exhaled as waste. Reactions in mineral compartments produce acetate, amino acids, and the components of nucleosides. Short peptides, condensed from the simple amino acids, sequester ‘ready-made’ iron sulfide clusters to form protoferredoxins, and also bind phosphates. Nucleotides are assembled from amino acids, simple phosphates carbon dioxide and ribose phosphate upon nanocrystalline mineral surfaces. The side chains of particular amino acids register to fitting nucleotide triplet clefts. Keyed in, the amino acids are polymerized, through acid–base catalysis, to alpha chains. Peptides, the tenuous outer-most filaments of the nanocrysts, continually peel away from bound RNA. The polymers are concentrated at cooler regions of the mineral compartments through thermophoresis. RNA is reproduced through a convective polymerase chain reaction operating between 40 and 100°C. The coded peptides produce true ferredoxins, the ubiquitous proteins with the longest evolutionary pedigree. They take over the role of catalyst and electron transfer agent from the iron sulfides. Other iron–nickel sulfide clusters, sequestered now by cysteine residues as CO-dehydrogenase and acetyl-coenzyme-A synthase, promote further chemosynthesis and support the hatchery—the electrochemical reactor—from which they sprang. Reactions and interactions fall into step as further pathways are negotiated. This hydrothermal circuitry offers a continuous supply of material and chemical energy, as well as electricity and proticity at a potential appropriate for the onset of life in the dark, a rapidly emerging kinetic structure born to persist, evolve and generate entropy while the sun shines. (shrink)

Collectins, present in plasma and on mucosal surfaces, are humoral molecules of the innate immune system. They were discovered a hundred years ago in 1906 as the first association of an animal lectin with the immune system. They are a family of calcium‐dependent lectins that recognize pathogen‐associated molecular patterns. They share a similar modular domain architecture consisting of four regions; a cysteine‐rich N‐terminal domain, a collagen‐like region, an α‐helical neck domain and a C‐terminal carbohydrate recognition domain. There have been (...) eight collectins members defined so far, of which, MBL, SP‐A and SP‐D are the most characterized. Collectins represent the first line of host defense. Upon recognition of the infectious agents, collectins put into action effector mechanisms like direct opsonization, neutralization, agglutination, complement activation and phagocytosis to curb the microbial growth. In addition, they also modulate inflammatory and allergic responses and apoptotic cell clearance. These functions limit infection and subsequently modulate the adaptive immune responses. The role of collectins, their structure, function, characteristics and clinical significance are reviewed in this article. BioEssays 29:452–464, 2007. © 2007 Wiley Periodicals, Inc. (shrink)

Metallothioneins (MTs) are ubiquitous proteins with the capacity to bind heavy metal ions (mainly Cd, Zn or Cu), and they have been found in animals, plants, eukaryotic and prokaryotic micro‐organisms. We have carried out a comparative analysis of ciliate MTs (Tetrahymena species) to well‐known MTs from other organisms, discussing their exclusive features, such as the presence of aromatic amino acid residues and almost exclusive cysteine clusters (CCC) present in cadmium‐binding metallothioneins (CdMTs), higher heavy metal‐MT stoichiometry values, and a strictly (...) conserved modular–submodular structure. Based on this last feature and an extensive gene duplication, we propose a possible model for the evolutionary history of T. thermophila MTs. We also suggest possible functions for these MTs from consideration of their differential gene expressions and discuss the potential use of these proteins and/or their gene promoters for designing molecular or whole‐cell biosensors for a fast detection of heavy metals in diverse polluted ecosystems. (shrink)

Secreted Frizzled‐related proteins (SFRPs) are modulators of the intermeshing pathways in which signals are transduced by Wnt ligands through Frizzled (Fz) membrane receptors. The Wnt networks influence biological processes ranging from developmental cell fate, cell polarity and adhesion to tumorigenesis and apoptosis. In the five or six years since their discovery, the SFRPs have emerged as dynamically expressed proteins able to bind both Wnts and Fz, with distinctive structural properties in which cysteine‐rich domains from Fz‐ and from netrin‐like proteins (...) are juxtaposed. The abundant expression of SFRP genes in the early embryo, altered expression patterns in disease states, and potential significance in the evolution of the vertebrate body plan, make these intriguing molecules relevant to investigations in diverse fields of biology and biomedical sciences. BioEssays 24:811–820, 2002. © 2002 Wiley Periodicals, Inc. (shrink)

Retroviruses encode a small, basic nucleocapsid (NC) protein that is found complexed to genomic RNA within the viral particle. The NC protein appears to function not only in a histone‐like manner in packaging the RNA into the particle but also in specifically selecting the viral genomic RNA for packaging. A cysteine‐histidine (cys‐his) region, usually composed of 14 amino acids and reminiscent of the ‘zinc fingers’ of transcription factors, is the only highly conserved sequence element among the retroviral NC proteins. (...) This review discusses the biochemical properties of NC, and its possible role(s) in retroviral replication. We also speculate on how the biochemical properties may relate to its function in RNA recognition and packaging. (shrink)

Methionine aminopeptidases with a universal specificity have been revealed from the sequences of the amino‐terminal region of mutant forms of yeast iso‐1‐cytochrome c and from a systematic examination of the literature for amino‐terminal sequences formed at initiation sites. The aminopeptidase removes amino‐terminal residues of methionine when they precede certain amino acids, with a specificity that appears to be determined mainly by the residue adjacent to the methionine residue at the amino terminus. The result with the mutationally altered iso‐1‐cytochromes c and (...) the results from published sequences of other proteins from a wide range of prokaryotes and eukaryotes suggest that the aminopeptidase usually cleaves amino‐terminal methionine when it precedes residues of alanine, cysteine, glycine, proline, serine, threonine and valine but not when it precedes residues of arginine, asparagine, aspartic acid, glutamine, glutamic acid, isoleucine, leucine, lysine or methionine. We suggest that the specificity is almost always determined simply by the size of the side chain of the penultimate residue; methionine is usually cleaved from residues with a side chain having a radius of gyration of 1·29 Å or less, but is not cleaved from residues with larger side chains. (shrink)

The prenylated proteins represent a newly discovered class of post‐translationally modified proteins. The known prenylated proteins include the oncogene product p21ras and other low molecular weight GTP‐binding proteins, the nuclear lamins, and the γ subunit of the heterotrimeric G proteins. The modification involves the covalent attachment of a 15‐carbon (farnesyl) or 20‐carbon (geranylgeranyl) isoprenoid moiety in a thioether linkage to a carboxyl terminal cysteine. The nature of the attached substituent is dependent on specific sequence information in the carboxyl terminus (...) of the protein. In addition, prenylation entrains other post‐translational modifications forming a reaction pathway. In this article, we review our current understanding of the biochemical reactions involved in prenylation and discuss the possible role of this modification in the control of cellular functions such as protein maturation and cell growth. (shrink)

The gut protozoan parasite, Giardia duodenalis, is the best characterized example of the most ancient eukaryotes, which are anaerobic and appear to be primitively amitochondrial. Apart from its obvious medical importance, Giardia is fascinating in its own right. Its prokaryotic-like anaerobic metabolism renders it selectively sensitive to some bacterial drugs, especially the nitroimidazoles, which are activated to form toxic radicals. Other features, including an enzyme that reduces oxygen directly to water, cysteine as the keeper of redox balance, a plasmid, (...) and toxin-like genes are also distinctly prokaryotic-like. But, unlike prokaryotes, Giardia has a sophisticated, highly developed cytoskeleton, bounded nuclei, linear chromosomes capped with telomeric repeats, and telomere positional regulation of gene expression. BioEssays 20:256–263, 1998.© 1998 John Wiley & Sons, Inc. (shrink)

The vav proto‐oncogene encodes a 95 kDa protein which is expressed exclusively in hematopoietic cells. Analysis of the deduced amino acid sequence has revealed the presence of a src‐homology 2 (SH2) domain, 2 SH3 domains, a cysteine‐rich region with similarity to protein kinase C, and a region highly similar to proteins with guanine nucleotide exchange activity on ras‐like GTPases. Recent work has shown that vav is tyrosine phosphorylated in response to stimulation of surface membrane receptors in a variety of (...) hematopoietic cell lines. Vav may play a role in hematopoietic cell signaling by coupling tyrosine kinase pathways to ras‐like GTPases through the regulation of guanine nucleotide exchange. (shrink)