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Infect. Immun., Jan 1998, 181-190, Vol 66, No. 1
K Poulsen, J Reinholdt, C Jespersgaard, K Boye, TA Brown, M Hauge and M Kilian
An analysis of 13 immunoglobulin A1 (IgA1) protease genes (iga) of strains
of Streptococcus pneumoniae, Streptococcus oralis, Streptococcus mitis, and
Streptococcus sanguis was carried out to obtain information on the
structure, polymorphism, and phylogeny of this specific protease, which
enables bacteria to evade functions of the predominant Ig isotype on
mucosal surfaces. The analysis included cloning and sequencing of iga genes
from S. oralis and S. mitis biovar 1, sequencing of an additional seven iga
genes from S. sanguis biovars 1 through 4, and restriction fragment length
polymorphism (RFLP) analyses of iga genes of another 10 strains of S. mitis
biovar 1 and 6 strains of S. oralis. All 13 genes sequenced had the
potential of encoding proteins with molecular masses of approximately 200
kDa containing the sequence motif HEMTH and an E residue 20 amino acids
downstream, which are characteristic of Zn metalloproteinases. In addition,
all had a typical gram-positive cell wall anchor motif, LPNTG, which, in
contrast to such motifs in other known streptococcal and staphylococcal
proteins, was located in their N-terminal parts. Repeat structures showing
variation in number and sequence were present in all strains and may be of
relevance to the immunogenicities of the enzymes. Protease activities in
cultures of the streptococcal strains were associated with species of
different molecular masses ranging from 130 to 200 kDa, suggesting
posttranslational processing possibly as a result of autoproteolysis at
post-proline peptide bonds in the N- terminal parts of the molecules.
Comparison of deduced amino acid sequences revealed a 94% similarity
between S. oralis and S. mitis IgA1 proteases and a 75 to 79% similarity
between IgA1 proteases of these species and those of S. pneumoniae and S.
sanguis, respectively. Combined with the results of RFLP analyses using
different iga gene fragments as probes, the results of nucleotide sequence
comparisons provide evidence of horizontal transfer of iga gene sequences
among individual strains of S. sanguis as well as among S. mitis and the
two species S. pneumoniae and S. oralis. While iga genes of S. sanguis and
S. oralis were highly homogeneous, the genes of S. pneumoniae and S. mitis
showed extensive polymorphism reflected in different degrees of antigenic
diversity.
Copyright © 1998, American Society for Microbiology
A comprehensive genetic study of streptococcal immunoglobulin A1 proteases: evidence for recombination within and between species
Department of Medical Microbiology, University of Aarhus, Denmark. mikrkp@svfcd.aau.dk
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