A role for LHC1 in higher order structure and complement binding of the Cryptococcus neoformans capsule.

Yoon-Dong Park,Jin Qiu,John Panepinto,David Beenhouwer,Soowan Shin,Uwe Himmelreich,John E Bennett,Peter R Williamson,Nannan Zhang,Patricia Albuquerque,Jeanie Ramos,Susana Frases,Arturo Casadevall,Radames J B Cordero,Robin Charles May

doi:10.1371/journal.ppat.1004037

Abstract

Polysaccharide capsules are important virulence factors for many microbial pathogens including the opportunistic fungus Cryptococcus neoformans. In the present study, we demonstrate an unusual role for a secreted lactonohydrolase of C. neoformans, LHC1 in capsular higher order structure. Analysis of extracted capsular polysaccharide from wild-type and lhc1Δ strains by dynamic and static light scattering suggested a role for the LHC1 locus in altering the capsular polysaccharide, both reducing dimensions and altering its branching, density and solvation. These changes in the capsular structure resulted in LHC1-dependent alterations of antibody binding patterns, reductions in human and mouse complement binding and phagocytosis by the macrophage-like cell line J774, as well as increased virulence in mice. These findings identify a unique molecular mechanism for tertiary structural changes in a microbial capsule, facilitating immune evasion and virulence of a fungal pathogen.

Highlights

Polysaccharide capsules (PC) are highly diverse hydrated structures that provide microbes with a key defense against the host immune system [1]
To evaluate the consequences of the reduced LHC1-dependent complement binding in C. neoformans, we modeled the studies in mice, a species that would allow testing for virulence [35]
The cryptococcal capsule is large and complex, resulting in cells with diameters up to 50 mm in diameter that cannot be ingested by phagocytic cells [37]

Summary

Introduction

Polysaccharide capsules (PC) are highly diverse hydrated structures that provide microbes with a key defense against the host immune system [1]. A prominent virulence factor of the opportunistic pathogen Cryptococcus neoformans is a large polysaccharide capsule with potent anti-phagocytic properties [4]. Extensive work by numerous investigators has provided key insights into synthesis and virulence role of the capsular primary structure [7]. Genes controlling or regulating higher order structures of the capsular polysaccharide have not been identified. This has been in part due to difficulties in assessing the tertiary structure of the cryptococcal polysaccharide

Methods

Results

Conclusion