title: The betagamma-crystallin superfamily contains a universal motif for binding calcium.
abstract: The betagamma-crystallin superfamily consists of evolutionarily related proteins with domain topology similar to lens beta- and gamma-crystallins, formed from duplicated Greek key motifs. Ca(2+) binding was found in a few betagamma-crystallin members earlier, although its prevalence and diversity as inherent molecular properties among members of the superfamily are not well studied. To increase our understanding of Ca(2+) binding in various betagamma-crystallins, we undertook comprehensive structural and Ca(2+)-binding studies of seven members of the superfamily from bacteria, archaea, and vertebrates, including determination of high-resolution crystal structures of three proteins. Our structural observations show that the determinants of Ca(2+) coordination remain conserved in the form of an N/D-N/D-#-I-S/T-S motif in all domains. However, binding of Ca(2+) elicits varied physicochemical responses, ranging from passive sequestration to active stabilization. The motif in this superfamily is modified in some members like lens crystallins where Ca(2+)-binding abilities are partly or completely compromised. We show that reduction or loss of Ca(2+) binding in members of the superfamily, particularly in vertebrates, is due to the selective presence of unfavorable amino acids (largely Arg) at key Ca(2+)-ligation positions and that engineering of the canonical Ca(2+)-binding residues can confer binding activity on an otherwise inactive domain. Through this work, we demonstrate that betagamma-crystallins with the N/D-N/D-#-I-S/T-S motif form an extensive set of Ca(2+)-binding proteins prevalent in all of the three kingdoms of life.
authors.affiliation: Centre for Cellular and Molecular Biology, Council of Scientific and Industrial Research, Uppal Road, Hyderabad 500007, India.
authors.forename: Penmatsa
authors.initials: P
authors.lastname: Aravind
authors.forename: Amita
authors.initials: A
authors.lastname: Mishra
authors.forename: Shashi Kumar
authors.initials: SK
authors.lastname: Suman
authors.forename: Maroor K
authors.initials: MK
authors.lastname: Jobby
authors.forename: Rajan
authors.initials: R
authors.lastname: Sankaranarayanan
authors.forename: Yogendra
authors.initials: Y
authors.lastname: Sharma
mesh_terms: D020816:Amino Acid Motifs; D000595:Amino Acid Sequence; D000818:Animals; D019843:Archaeal Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D001426:Bacterial Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D001665:Binding Sites; D002118:Calcium / Q000737:chemistry*; D056890:Eukaryota / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D019143:Evolution, Molecular; D008969:Molecular Sequence Data; D005810:Multigene Family; D011485:Protein Binding; D016415:Sequence Alignment; D038222:gamma-Crystallins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism
chemical_list: D019843:Archaeal Proteins; D001426:Bacterial Proteins; D038222:gamma-Crystallins; D002118:Calcium