Rj. Trevino et al., TRUNCATIONS AT THE NH2 TERMINUS OF RHODANESE DESTABILIZE THE ENZYME AND DECREASE ITS HETEROLOGOUS EXPRESSION, The Journal of biological chemistry, 273(43), 1998, pp. 27841-27847
Rhodanese mutants containing sequential NH2-terminal deletions were co
nstructed to test the distinct contributions of this region of the pro
tein to expression, folding, and stability. The results indicate that
the first 11 residues are nonessential for folding to the active confo
rmation, but they are necessary for attaining an active, stable struct
ure when expressed in Escherichia coli, Rhodanese species with up to 9
residues deleted were expressed and purified. Kinetic parameters for
the mutants were similar to those of the full-length enzyme. Compared
with shorter truncations, mutants missing 7 or 9 residues were (a) inc
reasingly inactivated by urea denaturation, (b) more susceptible to in
activation by dithiothreitol, (c) less able to be reactivated, and (d)
less rapidly inactivated by incubation at 37 degrees C, Immunoprecipi
tation showed that mutants lacking 10-23 NH2-terminal amino acids were
expressed as inactive species of the expected size but were rapidly e
liminated. Cell-free transcription/translation at 37 degrees C showed
mutants deleted through residue 9 were enzymatically active, but they
were inactive when deleted further, just as in vivo, However, at 30 de
grees C in vitro, both Delta 1-10 and Delta 1-11 showed considerable a
ctivity. Truncations in the NH2 terminus affect the chemical stability
of the distantly located active site. Residues Ser-11 through Gly-22,
which form the NH2-proximal alpha-helix, contribute to folding to an
active conformation, to resisting degradation during heterologous expr
ession, and to chemical stability in vitro.