Insights into protein adaptation to a saturated salt environment from the crystal structure of a halophilic 2Fe-2S ferredoxin.
Haloarcula marismortui is an archaebacterium that flourishes in the world's saltiest body of water, the Dead Sea. The cytosol of this organism is a supersaturated salt solution in which proteins are soluble and active. The crystal structure of a 2Fe-2S ferredoxin from H. marismortui determined at 1.9 A is similar to those of plant-type 2Fe-2S ferredoxins of known structure, with two important distinctions. The entire surface of the protein is coated with acidic residues except for the vicinity of the iron-sulphur cluster, and there is an insertion of two amphipathic helices near the N-terminus. These form a separate hyperacidic domain whose postulated function to provide extra surface carboxylates for solvation. These data and the fact that bound surface water molecules have on the average 40% more hydrogen bonds than in a typical non-halophilic protein crystal structure support the notion that haloadaptation involves better water binding capacity.
Frolow
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Department of Structural Biology, The Weizmann Institute of Science, Rehovot, Israel.
Harel
M
M
Sussman
J L
JL
Mevarech
M
M
Shoham
M
M
D000220:Adaptation, Biological; D000595:Amino Acid Sequence; D000596:Amino Acids / Q000032:analysis; D003198:Computer Simulation; D018360:Crystallography, X-Ray; D005288:Ferredoxins / Q000737:chemistry* / Q000145:classification; D006216:Halobacteriaceae / Q000737:chemistry*; D008958:Models, Molecular; D008969:Molecular Sequence Data; D010944:Plants / Q000737:chemistry; D017386:Sequence Homology, Amino Acid; D013499:Surface Properties; D014867:Water / Q000737:chemistry
C081714:2Fe-2S ferredoxin; D000596:Amino Acids; D005288:Ferredoxins; D014867:Water