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ARE PROTEIN FOLDING
INTERMEDIATES CAUSED BY TRANSIENT AGGREGATION ?
Maria Silow, Avd.
för Biokemi Ideon G2:G Sölvegatan 41 223 63 Lund
Mia Silow and Mikael Oliveberg, Biochemistry, Chemical Centre,
BOX 124, S-221 00 Lund, Sweden. e-mail:
mikael.oliveberg@biochem.lu.se
Recently some small globular proteins have been found
to fold directly into their native conformations in a two-state
process without populated intermediates. The findings question
the
role of intermediates and point at the possibility that partly
structured states are misfolds trapped in non-productive
pathways. We
report here that the spliceosomal protein U1A, which exhibits a
classical three-state folding behaviour, has an intermediate
which is
caused by transient aggregation of denatured protein. The
aggregation
behaviour is reflected in a concentration dependence of the
refolding
amplitudes. At low concentrations of protein, U1A folds in a
two-state process directly from the denatured monomer whereas at
high
concentrations of protein the observed refolding takes place from
an
aggregate which is formed in the dead-time of the stopped-flow
instrument. Is transient aggregation a general problem in time
resolved folding studies or a unique feature of the polypeptide
of U!
1A ?
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