Structural adaptation of enzymes to low temperatures.
A systematic comparative analysis of 21 psychrophilic enzymes belonging to different structural families from prokaryotic and eukaryotic organisms is reported. The sequences of these enzymes were multiply aligned to 427 homologous proteins from mesophiles and thermophiles. The net flux of amino acid exchanges from meso/thermophilic to psychrophilic enzymes was measured. To assign the observed preferred exchanges to different structural environments, such as secondary structure, solvent accessibility and subunit interfaces, homology modeling was utilized to predict the secondary structure and accessibility of amino acid residues for the psychrophilic enzymes for which no experimental three-dimensional structure is available. Our results show a clear tendency for the charged residues Arg and Glu to be replaced at exposed sites on alpha-helices by Lys and Ala, respectively, in the direction from 'hot' to 'cold' enzymes. Val is replaced by Ala at buried regions in alpha-helices. Compositional analysis of psychrophilic enzymes shows a significant increase in Ala and Asn and a decrease in Arg at exposed sites. Buried sites in beta-strands tend to be depleted of VAL: Possible implications of the observed structural variations for protein stability and engineering are discussed.
Gianese
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Dipartimento di Scienze Biochimiche A. Rossi Fanelli and Centro di Biologia Molecolare del CNR , P.le A. Moro 5, 00185 Rome, Italy.
Argos
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P
Pascarella
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D000409:Alanine / Q000737:chemistry; D019943:Amino Acid Substitution; D000596:Amino Acids / Q000737:chemistry*; D001216:Asparagine / Q000737:chemistry; D002384:Catalysis; D003080:Cold Temperature; D004795:Enzyme Stability; D004798:Enzymes / Q000737:chemistry* / Q000145:classification; D005057:Eukaryotic Cells / Q000201:enzymology*; D008239:Lysine / Q000737:chemistry; D008956:Models, Chemical; D011387:Prokaryotic Cells / Q000201:enzymology*; D015202:Protein Engineering; D017433:Protein Structure, Secondary; D016415:Sequence Alignment; D020539:Sequence Analysis, Protein; D013329:Structure-Activity Relationship; D013816:Thermodynamics
D000596:Amino Acids; D004798:Enzymes; D001216:Asparagine; D008239:Lysine; D000409:Alanine