S. Kangsadalampai et al., Identification and characterization of two missense mutations causing factor XIIIA deficiency, BR J HAEM, 104(1), 1999, pp. 37-43
In this study, two amino acid substitutions, Arg260His and Val414Phe, have
been identified in the factor XIIIA subunits of factor XIII deficient patie
nts of Syrian and Indian descent, respectively. To confirm the deleterious
effects of these substitutions, both variant sequences have been engineered
into cDNA clones and the mutant enzymes expressed in yeast. Determination
of the transglutaminase activity and immune detection of the mutant enzymes
together with mRNA hybridization revealed that the mutations dramatically
reduce both the catalytic activity and the level of enzyme expressed in yea
st. The mutations Arg260His and Val414Phe occur within the 'core' domain of
the enzyme. Computer modelling of the mutant enzymes reveals that the subs
titution of the Arg260 by His results in the loss of a conserved electrosta
tic interaction whereas the effect of the Val414Phe substitution is a conse
quence of the large increase in side-chain volume. Although both mutations
do not effect the active site directly, they are predicted to reduce the st
ability of the enzyme.
The effects of these two amino acid substitutions on enzyme expression and
three-dimensional structure strongly confirm that residues which are locate
d outside of the active site can have a significant effect on protein stabi
lity and function.