Three hydrophobic surface binding a proteins link surface hydrophobicity to sporulation, biofilm formation, and host interaction in Mucor lusitanicus.

INTRODUCTION: Mucor lusitanicus is a model organism for studying fungal development and physiology, as well as pathogenicity of Mucorales fungi. Hydrophobic surface-binding proteins (HsbA family) have been described in filamentous fungi as interface-associated factors involved in adhesion, enzymatic recruitment, and surface interactions; however, their functional diversification in Mucorales remains poorly understood.

METHODS: Here, we present a comprehensive characterization of three HsbA proteins in M. lusitanicus.

RESULTS: All examined HsbA proteins share a conserved α-helical fold with a hydrophobic core and are capable of binding fatty acids, while displaying differential affinity for hydrophobic interfaces.

DISCUSSION: These structural properties translate into distinct surface-associated functions, including modulation of surface hydrophobicity, biofilm formation, and sporangial architecture. Genetic analyses further demonstrate that HsbA proteins play a central role in developmental regulation, affecting spore germination timing, stress responses, sporulation, and spore hydrophobicity. At the host interaction level, HsbA overexpression increases early phagocytic uptake but impairs infection progression, whereas gene disruption enhances virulence in in vivo insect models. These findings support a model in which HsbA proteins primarily regulate developmental timing rather than acting as classical virulence determinants. Collectively, our results show that HsbA proteins in M. lusitanicus function as regulators that couple fungal surface remodeling with developmental transitions. Unlike previously characterized fungal surface systems that mainly mediate adhesion, immune evasion, or enzymatic recruitment, Mucor HsbA proteins integrate surface properties with growth timing, thereby coordinating environmental adaptation and host-pathogen interactions.