Asp30 of Aspergillus oryzae cutinase CutL1 is involved in the ionic interaction with fungal hydrophobin RolA

Aspergillus oryzae hydrophobin RolA adheres to the biodegradable polyester polybutylene succinate-co-adipate (PBSA) and promotes PBSA degradation by interacting with A. oryzae polyesterase CutL1 and recruiting it to the PBSA surface. In our previous studies, we found that positively charged amino acid residues (H32, K34) of RolA and negatively charged residues (E31, D142, D171) of CutL1 are important for the cooperative ionic interaction between RolA and CutL1, but some other charged residues in the triple mutant CutL1-E31S/D142S/ D171S are also involved. In the present study, on the basis of the 3D-structure of CutL1, we hypothesized that D30 is also involved in the CutL1–RolA interaction. We substituted D30 with serine and performed kinetic analysis of the interaction between wild-type RolA and the single mutant CutL1-D30S or quadruple mutant CutL1-D30S/E31S/D142S/ D171S by using quartz crystal microbalance. Our results indicate that D30 is a novel residue involved in the ionic interaction between RolA and CutL1.