Novel Hydrophobic Surface Binding Protein, HsbA, Produced by Aspergillus oryzae

Hydrophobic surface binding protein A (HsbA) is a secreted protein (14.5 kDa) isolated from the culture broth ofAspergillus oryzae RIB40 grown in a medium containing polybutylene succinate-co -adipate (PBSA) as a sole carbon source. We purified HsbA from the culture broth and determined its N-terminal amino acid sequence. We found a DNA sequence encoding a protein whose N terminus matched that of purified HsbA in theA. ozyzae genomic sequence. We cloned thehsbA genomic DNA and cDNA fromA. oryzae and constructed a recombinantA. oryzae strain highly expressinghsbA . Orthologues of HsbA were present in animal pathogenic and entomopathogenic fungi. Heterologously synthesized HsbA was purified and biochemically characterized. Although the HsbA amino acid sequence suggests that HsbA may be hydrophilic, HsbA adsorbed to hydrophobic PBSA surfaces in the presence of NaCl or CaCl2 . When HsbA was adsorbed on the hydrophobic PBSA surfaces, it promoted PBSA degradation via the CutL1 polyesterase. CutL1 interacts directly with HsbA attached to the hydrophobic QCM electrode surface. These results suggest that when HsbA is adsorbed onto the PBSA surface, it recruits CutL1, and that when CutL1 is accumulated on the PBSA surface, it stimulates PBSA degradation. We previously reported that when theA. oryzae hydrophobin RolA is bound to PBSA surfaces, it too specifically recruits CutL1. Since HsbA is not a hydrophobin,A. oryzae may use several types of proteins to recruit lytic enzymes to the surface of hydrophobic solid materials and promote their degradation.