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Applied and Environmental Microbiology, April 1999, p. 1390-1396, Vol. 65, No. 4
Department of Biophysical Chemistry,
Netherlands Institute for Dairy Research (NIZO), 6710 BA Ede, The
Netherlands
Received 13 August 1997/Accepted 11 September 1998
The mature lactococcal cell envelope proteinase (CEP) consists of
an N-terminal subtilisin-like proteinase domain and a large C-terminal
extension of unknown function whose far end anchors the molecule in the
cell envelope. Different types of CEP can be distinguished on the basis
of specificity and amino acid sequence. Removal of weakly bound
Ca2+ from the native cell-bound CEP of Lactococcus
lactis SK11 (type III specificity) is coupled with a significant
reversible decrease in specific activity and a dramatic reversible
reduction in thermal stability, as a result of
which no activity at 25°C (pH 6.5) can be measured. The consequences
of Ca2+ removal are less dramatic for the CEP of strain
Wg2 (mixed type I-type III specificity). Autoproteolytic release
of CEP from cells concerns this so-called "Ca-free" form
only and occurs most efficiently in the case of the Wg2 CEP. The
results of a study of the relationship between the Ca2+
concentration and the stability and activity of the cell-bound SK11 CEP
at 25°C suggested that binding of at least two Ca2+ ions
occurred. Similar studies performed with hybrid CEPs constructed from
SK11 and Wg2 wild-type CEPs revealed that the C-terminal extension
plays a determinative role with respect to the ultimate distinct
Ca2+ dependence of the cell-bound CEP. The results are
discussed in terms of predicted Ca2+ binding sites in the
subtilisin-like proteinase domain and Ca-triggered structural
rearrangements that influence both the conformational stability of the enzyme and the effectiveness of the catalytic site. We
argue that distinctive primary folding of the proteinase domain is
guided and maintained by the large C-terminal extension.
0099-2240/99/$04.00+0
Copyright © 1999, American Society for Microbiology. All rights reserved.
Role of Calcium in Activity and Stability of
the Lactococcus lactis Cell Envelope
Proteinase
*
Corresponding author. Mailing address: NIZO, P.O. Box
20, 6710 BA Ede, The Netherlands. Phone: 31-318-659534. Fax:
31-318-650400. E-mail: exterkate{at}nizo.nl.
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