The accessory Sec system (SecY2A2) in Streptococcus pneumoniae is involved in export of pneumolysin toxin, adhesion and biofilm formation

Mikaila Bandara,J Mark Skehel,Aras Kadioglu,Ian Collinson,Angela H Nobbs,Ariel J Blocker,Howard F Jenkinson

doi:10.1016/j.micinf.2017.04.003

Abstract

In Streptococcus pneumoniae TIGR4, genes encoding a SecY2A2 accessory Sec system are present within a locus encoding a serine-rich repeat surface protein PsrP. Mutant strains deleted in secA2 or psrP were deficient in biofilm formation, while the ΔsecA2 mutant was reduced in binding to airway epithelial cells. Cell wall protein (CWP) fractions from the ΔsecA2 mutant, but not from the ΔpsrP mutant, were reduced in haemolytic (pneumolysin) activity. Contact-dependent pneumolysin (Ply) activity of wild type TIGR4 cells was ten-fold greater than that of ΔsecA2 mutant cells suggesting that Ply was not active at the ΔsecA2 cell surface. Ply protein was found to be present in the CWP fraction from the ΔsecA2 mutant, but showed aberrant electrophoretic migration indicative of protein modification. Proteomic analyses led to the discovery that the ΔsecA2 mutant CWP fraction was deficient in two glycosidases as well as other enzymes involved in carbohydrate metabolism. Taken collectively the results suggest that positioning of Ply into the cell wall compartment in active form, together with glycosyl hydrolases and adhesins, requires a functional accessory Sec system.

Highlights

Streptococcus pneumoniae, known as the pneumococcus, colonizes the human respiratory tract
Strain UB2570 DsecA2 cells showed no detectable differences in chain length, autoaggregation or growth rate compared to wild type TIGR4 (Fig. 2)
Biofilms formed by strains TIGR4, UB2570 DsecA2 and UB2312 DpsrP, the latter abrogated in serine-rich repeat (SRR) glycoprotein PsrP, were compared morphologically and quantitatively

Summary

Introduction

Streptococcus pneumoniae, known as the pneumococcus, colonizes the human respiratory tract. This can be asymptomatic, but in more susceptible individuals e.g. infants, the elderly, immunocompromised, the bacteria can move to other body sites and cause sinusitis, otitis media, pneumonia or meningitis. A confounding issue about the production of Ply is that, unlike other CDC family members, Ply lacks an N-terminal leader peptide to direct secretion through the canonical Sec pathway. It has been considered an intracellular protein, released only following cell lysis in vitro or in vivo [15]. The precise mechanism for Ply export across the cell membrane has not yet been established

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Results

Conclusion