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Title
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Refined crystal structure of lysozyme from the rainbow trout (Oncorhynchus mykiss).
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Authors
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S.Karlsen,
B.E.Eliassen,
L.K.Hansen,
R.L.Larsen,
B.W.Riise,
A.O.Smalås,
E.Hough,
B.Grinde.
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Ref.
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Acta Crystallogr D Biol Crystallogr, 1995,
51,
354-367.
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PubMed id
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Abstract
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Lysozymes (E.C. 3.2.1.17) are well characterized ubiquitous enzymes that have an
antibacterial effect. The lysozymes from rainbow trout (RBTL) (Oncorhynchus
mykiss) could be particularly interesting in aquaculture since they show higher
activity than egg-white lysozyme and lysozymes from other fish species against a
variety of pathogenic bacteria. Two lysozymes, I and II, differing only in a
single amino acid, were purified from the kidney of rainbow trout and shown to
belong to the c-type class of lysozymes. The type II form was shown to be much
more potent against a variety of bacteria than the type I enzyme. We have grown
crystals from a mixture containing about 80% type I and 20% type II lysozyme
from rainbow trout, and solved the X-ray crystal structure. The crystals are
trigonal with a = 76.68, c = 54.46 A and space group P3(1)21. The phase problem
was solved by the molecular-replacement method, and the structure was refined to
an R-factor of 17.4% using data to 1.8 A resolution. The crystal structure shows
that the three-dimensional structure of rainbow trout lysozyme is very similar
to the previously solved structures of other c-type lysozymes. The single
polypeptide of 129 amino acids is folded into two domains separated by a deep
cleft which contains the active site. Secondary-structure elements, four
alpha-helices and a three-stranded beta-sheet, are located in the same
sequential positions as in the hen, turkey and human enzymes. The beta-sheet is
found to be common for structures of both c- and g-type lysozymes. We suggest
that differences in antibiotic activity of the two forms of RBTL are probably
due to small differences in the hydophobicity of a small surface region.
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