Three-dimensional structure of a halotolerant algal carbonic anhydrase predicts halotolerance of a mammalian homolog

Abstract

Protein molecular adaptation to drastically shifting salinities was studied in dCA II, an ␣-type carbonic anhydrase (EC 4.2.1.1) from the exceptionally salt-tolerant unicellular green alga Dunaliella salina. The salt-inducible, extracellular dCA II is highly salt-tolerant and thus differs from its mesophilic homologs. The crystal structure of dCA II, determined at 1.86-Å resolution, is globally similar to other ␣-type carbonic anhydrases except for two extended ␣-helices and an added Na-binding loop. Its unusual electrostatic properties include a uniformly negative surface electrostatic potential of lower magnitude than that observed in the highly acidic halophilic proteins and an exceptionally low positive potential at a site adjoining the catalytic Zn 2؉ compared with mesophilic homologs. The halotolerant dCA II also differs from typical halophilic proteins in retaining conformational stability and solubility in low to high salt concentrations. The crucial role of electrostatic features in dCA II halotolerance is strongly supported by the ability to predict the unanticipated halotolerance of the murine CA XIV isozyme, which was confirmed biochemically. A proposal for the functional significance of the halotolerance of CA XIV in the kidney is presented.nonhalophilic ͉ protein salt adaptation ͉ x-ray structure

A Multicopper Ferroxidase Involved in Iron Binding to Transferrins in Dunaliella salina Plasma Membranes

“…All 14 amino acid sequences obtained by the MS analysis, covering about 12% of the total protein, were identified within the deduced amino acid sequence (data no shown). The highest sequence similarity (40% identity and 57% similarity) was obtained by FOX1, an iron-deficiency induced protein from the green alga C. reinhardtii ( Sequence Analysis of D-Fox-By comparing amino acid sequences of D-Fox to Fox1, we found 20% higher abundance of acidic residues, a characteristic feature of proteins in halophiles, which was also found previously in extracellular proteins of Dunaliella (18). Analysis of the deduced amino acid sequence of D-Fox revealed that it consists of three internal homologous repeats with 28 -31% sequence identity (amino acids 61-350, 400 -715, and 764-end), a typical feature in the MCO family, probably result- ing from a gene duplication event.…”

Characterization of a NaCl-tolerant β-N-acetylglucosaminidase from Sphingobacterium sp. HWLB1

“…Most NaCl-tolerant enzymes contain a high proportion of acidic amino acid residues Paul et al 2008;Premikumar et al 2005;Richard et al 2000). Carboxyl groups from acidic amino acid residues can bind more water molecules than other groups in a polypeptide and, thus, enable the polypeptide to form a particle stabilized by cooperative hydrated ion networks .…”

“…It is argued that salt bridge networks can recruit solvent chloride and sodium ions, and improve protein stability at high concentrations of NaCl (Richard et al 2000). The excess acidic amino acids in the protein composition could result in a large negatively charged surface and, finally, enhance the binding capacity of enzymes to water and salt ions Madern et al 2000;Premikumar et al 2005;Qin et al 2014;Shi et al 2013;Yamaguchi et al 2011). Similar to the NaCltolerant xylanase from Zunongwangia profunda , the catalytic pocket of Nag3HWLB1 also has higher negative electrostatic potentials than its homologs BsNagZ and StNagZ.…”

“…This unique feature of NaCltolerant enzymes has attracted considerable attention for basic research on their molecular adaptation to function in various applications Paul et al 2008;Premikumar et al 2005;Richard et al 2000). For example, NaCl-tolerant enzymes can be potentially used in processing sea foods and other foods with saline contents of 3.5-15.9 % (w/w) NaCl, such as marine materials, pickles, and sauces (Zhou et al 2015a).…”

Molecular Mechanisms of Enzyme Activation by Monovalent Cations

“…The architecture of these sites has been retained during evolution (6). Carbonic anhydrase of the halophile alga Dunaliella salina carries an added loop for specific Na ϩ binding that confers stability and resistance to high salinity (96). The loop is strikingly similar to the Na ϩ binding loop of thrombin (6), an enzyme that emerged much later from the deuterostome lineage and that utilizes Na ϩ not only for stability but also for optimal physiological function.…”