Human lysozyme has a structure similar to that
of hen lysozyme and differs in amino acid sequence by 51
out of 129 residues with one insertion at the position
between 47 and 48 in hen lysozyme. The backbone dynamics
of free or (NAG)3-bound human lysozyme has been
determined by measurements of 15N nuclear relaxation.
The relaxation data were analyzed using the Lipari–Szabo
formalism and were compared with those of hen lysozyme,
which was already reported (Mine S et al., 1999, J
Mol Biol 286:1547–1565). In this paper, it was
found that the backbone dynamics of free human and hen
lysozymes showed very similar behavior except for some
residues, indicating that the difference in amino acid
sequence did not affect the behavior of entire backbone
dynamics, but the folded pattern was the major determinant
of the internal motion of lysozymes. On the other hand,
it was also found that the number of residues in (NAG)3-bound
human and hen lysozymes showed an increase or decrease
in the order parameters at or near active sites on the
binding of (NAG)3, indicating the increase in
picosecond to nanosecond. These results suggested that
the immobilization of residues upon binding (NAG)3
resulted in an entropy penalty and that this penalty was
compensated by mobilizing other residues. However, compared
with the internal motions between both ligand-bound human
and hen lysozymes, differences in dynamic behavior between
them were found at substrate binding sites, reflecting
a subtle difference in the substrate-binding mode or efficiency
of activity between them.