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Publication Abstract from PubMed

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. Ca2+-binding was found in a few betagamma-crystallin members earlier, although its prevalence and diversity as an inherent molecular property among members of the superfamily is not well-studied. To increase our understanding of Ca2+-binding in various betagamma-crystallins, we undertook comprehensive structural and Ca2+-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 Ca2+ coordination remain conserved in the form of an N/D-N/D-#-I-S/T-S motif in all domains. However, binding of Ca2+ elicits varied physico-chemical responses, ranging from passive sequestration to active stabilization. The motif in this superfamily is modified in some members like lens crystallins where Ca2+-binding abilities are partly or completely compromised. We show that reduction or loss of Ca2+-binding in members of the superfamily, particularly in vertebrates, is due to the selective presence of unfavorable amino acids (largely Arg) at key Ca2+-ligation positions and that engineering of the canonical Ca2+-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 Ca2+-binding proteins prevalent in all the three kingdoms of life.

betagamma-Crystallin superfamily contains a universal motif for binding calcium.,Aravind P, Mishra A, Suman SK, Jobby MK, Sankaranarayanan R, Sharma Y Biochemistry. 2009 Nov 18. PMID:19921810^[1]

From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine.