Simulation Study of Candida rugosa Lipase Adsorption on Self-Assembled Monolayers

Candida rugosa lipase (CRL) is a versatile biocatalyst, and its immobilization on solid supports is widely used to improve its operational stability and reuse. Significantly, the adsorption orientation and adsorption-induced conformational rearrangements of CRL on charged surfaces can reshape the accessibility of the active site and the interfacial "lid" region, thereby directly governing the catalytic activity and durability of the immobilized enzyme. In this work, combined Parallel Tempering Monte Carlo (PTMC) and all-atom molecular dynamics (AAMD) simulations were employed to investigate the adsorption mechanism, orientation, and conformational changes of CRL on charged self-assembled monolayers (SAMs), including positively charged NH₂-SAMs and negatively charged COOH-SAMs, with different surface charge densities (SCD). The results indicate that electrostatic interactions dominate the adsorption process. CRL adopts a favorable "lying" orientation on the NH₂-SAM surface, which facilitates the exposure of its catalytic triad to the solution. In contrast, an "end-on" orientation is observed on the COOH-SAM surface, resulting in poor exposure of the active site. The NH₂-SAM surface exhibits strong adsorption intensity of CRL, and the enlargement of the active site entrance at low surface charge density may further promote its catalytic efficiency. Furthermore, the overall native conformation of CRL is well preserved upon adsorption. This study provides molecular-level insights into the controlled adsorption of CRL on charged surfaces and offers theoretical guidance for the rational design of lipase-immobilization carriers.