S. Karlsen et E. Hough, CRYSTAL-STRUCTURES OF 3 COMPLEXES BETWEEN CHITO-OLIGOSACCHARIDES AND LYSOZYME FROM THE RAINBOW-TROUT - HOW DISTORTED IS THE NAG SUGAR IN SITE-D, Acta crystallographica. Section D, Biological crystallography, 51, 1995, pp. 962-978
Citations number
56
Categorie Soggetti
Crystallography,"Biochemical Research Methods",Biology
Like all c-type lysozymes, those from rainbow trout act as 1,4-beta-ac
etyl-muramidases to destroy bacteria by cleaving the polysaccharide ch
ains of alternating N-acetylglucosamine (NAG) and N-acetylmuramic acid
(NAM) units in the cell walls. Lysozymes also hydrolyse chitin, the a
nalogous N-acetylglucosamine polymer. The rainbow trout enzymes have b
een shown to be particularly effective in bacterial defence. We have d
etermined the crystal structures of three complexes between rainbow tr
out lysozyme (RBTL) and the chito-oligosaccharides (NAG)(2), (NAG)(3)
and (NAG)(4) to resolutions of 1.8, 2.0 and 1.6 Angstrom, respectively
. Crystals of these complexes were obtained by co-crystallization, and
intensity data were collected on a FAST area detector system. Refinem
ent and model building gave final R values of 16.6, 15.9 and 16.5% for
the di-, tri- and tetrasaccharide complexes, respectively. The result
s show that the chito-oligosaccharides bind to sites A, B and C as pre
viously observed for complexes between the hen egg-white lysozyme (HEW
L) and a variety of saccharides. The NAG ring in site D is not bound s
o deeply and is only slightly distorted towards a half-chair conformat
ion as observed for the equivalent NAM residue in HEWL. From our resul
ts, there is reason to question the position and the degree of strain
of the D saccharide and the mode of binding and importance of two sacc
harides in sites E and F for correct orientation of sugar D and effect
ive hydrolysis of a productive substrate-lysozyme complex. Simple mode
l building study from our structures implies a 'left-sided' binding mo
de of (NAG)(6) in the lower part of the active site of RBTL.