The Aspergillus fumigatus cspA Gene Encoding a Repeat-Rich Cell Wall Protein Is Important for Normal Conidial Cell Wall Architecture and Interaction with Host Cells

Abstract

cspA (for cell surface protein A) encodes a repeat-rich glycophosphatidylinositol (GPI)-anchored cell wall protein (CWP) in the pathogenic fungus Aspergillus fumigatus. The number of repeats in cspA varies among isolates, and this trait is used for typing closely related strains of A. fumigatus. We have previously shown that deletion of cspA is associated with rapid conidial germination and reduced adhesion of dormant conidia. Here we show that cspA can be extracted with hydrofluoric acid (HF) from the cell wall, suggesting that it is a GPI-anchored CWP. The cspA-encoded CWP is unmasked during conidial germination and is surface expressed during hyphal growth. Deletion of cspA results in weakening of the conidial cell wall, whereas its overexpression increases conidial resistance to cell wall-degrading enzymes and inhibits conidial germination. Double mutant analysis indicates that cspA functionally interacts with the cell wall protein-encoding genes ECM33 and GEL2. Deletion of cspA together with ECM33 or GEL2 results in strongly reduced conidial adhesion, increased disorganization of the conidial cell wall, and exposure of the underlying layers of chitin and ␤-glucan. This is correlated with increasing susceptibility of the ⌬cspA, ⌬ECM33, and ⌬cspA ⌬ECM33 mutants to conidial phagocytosis and killing by human macrophages and hyphal damage induced by neutrophils. However, these strains did not exhibit altered virulence in mice with infected lungs. Collectively, these results suggest a role for cspA in maintaining the strength and integrity of the cell wall.

Adhesins in Human Fungal Pathogens: Glue with Plenty of Stick

“…Furthermore, none of the orthologous EPA genes in either strain are 100% identical. Relevant in this respect is the fact that the tandem repeat regions, which usually are present in fungal adhesin-encoding genes, frequently show strain-dependent size reductions or expansions occurring during DNA replication (23)(24)(25)96). All together, these intraspecies gene variations underline the extremely large genetic plasticity with respect to fungal adhesin genes, including the EPA family, in C. glabrata.…”

“…More recently, the GPI-modified wall protein CspA ("cell surface protein A") was identified as a putative adhesin with internal repeats (Table 2), of which the number per gene is strain dependent (96). The cspA-encoded cell wall protein is unmasked during conidial germination and is surface expressed during hyphal growth.…”

Fungal Morphogenesis

“…On germination and hyphal growth, cell wall protein CspA is unmasked, helping to mitigate hyphal damage induced by neutrophils (Levdansky et al 2010). Thus, factors produced during morphogenesis, in addition to the morphotype transition itself, help fungi adapt to host conditions.…”

Host Cell Invasion by Medically Important Fungi

“…Attempts to identify cell wall proteins with a role in host pathogen interactions have identified a number of candidate adhesins including CspA (Levdansky et al 2010), CfmA-C (Vaknin et al 2013), and CalA (Upadhyay et al 2009). Deletion of CspA or CfmA-C resulted in alterations in cell wall architecture and composition but did not affect host cell adherence or virulence, suggesting that these proteins play more of a structural role within the cell wall (Levdansky et al 2010;Vaknin et al 2013). Recombinant CalA was found to bind to laminin in vitro (Upadhyay et al 2009); however, a mutant deficient in CalA has not been tested for alterations in host cell binding or virulence, and thus the importance of this protein in host -pathogen interactions remains unknown.…”