Critical functional role of the COOH-terminal ends of longitudinal hydrophobic strips in alpha-helices of T4 lysozyme.
The sensitivity of bacteriophage T4 lysozyme function to amino acid substitutions at defined positions in and around the longitudinal, hydrophobic strips of 9 alpha-helices was assessed after systematic replacement of each residue in the protein with a series of 13 amino acids. The hydrophobic strips were defined by identifying the longitudinal sectors in the helices with the highest mean residue hydrophobicities. Sensitivity to mutation (the percentage of replacements leading to loss of function) was calculated for each residue in the following positions: whole protein, helices, hydrophobic strips, other positions within the helices, and various positions within the hydrophobic strips as well as their extensions beyond the helices. Substitutions at positions in the hydrophobic strips led more frequently to loss of function than substitutions in the protein as a whole. One subset, the COOH-terminal hydrophobic strip residues, is apparently critical; substitutions of these residues (but not of their NH2-terminal counterparts) led at least as frequently to loss of function as substitutions of solvent-inaccessible residues, and nearly as frequently as substitutions of the most highly conserved residues.
Rennell
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D
Department of Molecular Genetics, University of Massachusetts Medical School, Worcester 01655.
Poteete
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Beaulieu
M
M
Kuo
D Z
DZ
Lew
R A
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Humphreys
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D000465:Algorithms; D000595:Amino Acid Sequence; D004926:Escherichia coli / Q000201:enzymology; D005814:Genes, Viral; D008969:Molecular Sequence Data; D009113:Muramidase / Q000737:chemistry* / Q000378:metabolism; D016296:Mutagenesis; D011487:Protein Conformation; D012486:Salmonella typhimurium / Q000235:genetics; D013604:T-Phages / Q000201:enzymology* / Q000235:genetics; D010948:Viral Plaque Assay; D015678:Viral Structural Proteins / Q000235:genetics
D015678:Viral Structural Proteins; D009113:Muramidase