A. Coop et al., EFFECTS OF CONTROLLED MUTATIONS ON THE N-TERMINAL AND C-TERMINAL EXTENSIONS OF CHICK LENS BETA-B1 CRYSTALLIN, Graefe's archive for clinical and experimental ophthalmology, 236(2), 1998, pp. 146-150
Background: While gamma-crystallin exists as a monomer, beta-crystalli
n, which unlike gamma-crystallin contains N- and C-terminal arms, asso
ciates to form homodimers. Methods: In order to answer the question of
whether the extensions are involved in dimerisation of chick lens bet
a B1 crystallin, we have developed a heterologous expression system fo
r chicken beta B1 crystallin in Escherichia coli, and produced three m
utations by site-directed mutagenesis. We have substituted residues in
the PAPA segment of the N-terminal extension, curtailed the N-termina
l extension by five residues, and deleted 16 residues from the C-termi
nal extension. Results: High-resolution gel filtration chromatography
and non-denaturing gel electrophoresis show that the mutations did not
influence dimerisation of the beta B1 crystallin, while circular dich
roism and tryptophan fluorescence indicated that the mutations did not
have a major influence of beta B1 crystallin structure or its heat st
ability. Conclusions: Our experiments show that as with rat lens beta
B2 crystallin, dimerisation of beta B1 crystallin is not affected by a
lterations to the conserved PAPA region and that the peptide linker re
gion rather than the N- and C-terminal extensions must be important in
dimerisation.