A. Podbielski et al., A GROUP-A STREPTOCOCCAL ENN PROTEIN POTENTIALLY RESULTING FROM INTERGENOMIC RECOMBINATION EXHIBITS ATYPICAL IMMUNOGLOBULIN-BINDING CHARACTERISTICS, Molecular microbiology, 12(5), 1994, pp. 725-736
The gene encoding the Enn protein (enn) of the M untypeable group A st
reptococcal (GAS) strain 64/14 was amplified by polymerase chain react
ion, cloned into the expression vector pJLA602 and expressed in Escher
ichia cell DH5 alpha. Unlike other GAS-Enn proteins, which exhibit IgA
-binding activity, the recombinant Enn enn64/14 protein reacted prefer
entially with human IgG(3). The 1050 bp open reading frame comprising
the enn64/14 gene was completely sequenced. The region of the gene enc
oding the signal peptide and the C-terminus exhibited > 95% homology t
o corresponding sections of other enn genes. The region of enn64/14 en
coding the N-terminus of the mature Enn protein was found to be highly
homologous to the corresponding section of the gene encoding the M-li
ke protein of GAS serotype M9 (emmL9). The recombinant protein encoded
by emmL9 was found to react with all four human IgG subclasses. About
30% of the 1152bp open reading frame of emmL9 encoding the N-terminus
was found to display > 90% homology to the corresponding section of e
nn64/14 but was < 50% homologous in the remainder of the gene sequence
. The functional analysis of the subcloned N-terminal section of emmL9
demonstrated a polypeptide exhibiting selective binding to human IgG(
3). These findings suggested that enn64/14 was a hybrid gene formed by
recombination of an enn gene and an emmL9 gene. The putative recombin
ational event could have involved a set of Ranking 7bp direct repeats.
Since enn64/14 and emmL9 are genes from different phylogenetic lineag
es of GAS, this report provides evidence that intergenomic recombinati
ons between different types of GAS genes can occur and could lead to h
ybrid proteins with unique Ig-binding characteristics.