BspA is a basic surface-exposed protein from Lactobacillus fermentum BR11,
Sequence comp:comparisons have shown that it is a member of family III of t
he solute binding proteins. It is 89% identical to the collagen binding pro
tein, Cnb, from Lactobacillus reuteri, Compared with the database of Escher
ichia coli proteins, BspA, is most similar to the L-cystine binding protein
FliY. To investigate the function of BspA, mutants depleted for BspA were
generated by homologous recombination with a temperature-sensitive plasmid,
These mutants were significantly impaired in their abilities to take up L-
cystine. Uptake rates of L-glutamine, L-histidine, and L-lysine, which are
substrates for other binding proteins with similarity to BspA, were unaffec
ted. Evidence was obtained that BspA is necessary for maximal resistance to
oxidative stress. Specifically, inactivation of BspA causes defective grow
th in the presence of oxygen and sensitivity to paraquat, Measurements of s
ulfhydryl levels showed that incubation of L. fermentum BR11 with L-cystine
resulted in increased levels of sulfhydryl groups both inside and outside
the cell; however, this was not the case with a BspA mutant, The role of Bs
pA as an extracellular matrix protein adhesin was also addressed. L. fermen
tum BR11 does not bind to immobilized type I collagen or laminin above back
ground levels but does bind immobilized fibronectin. Inactivation of BspA d
id not significantly affect fibronectin binding; therefore, we have not fou
nd evidence to support the notion that BspA is an extracellular matrix prot
ein binding adhesin, As BspA is most probably not a lipoprotein, this repor
t provides evidence that gram-positive bacterial solute binding proteins do
not necessarily have to be anchored to the cytoplasmic membrane to functio
n in solute uptake.