A CALB-like Cold-Active Lipolytic Enzyme from Pseudonocardia antarctica: Expression, Biochemical Characterization, and AlphaFold-Guided Dynamics

Abstract

Cold-active lipolytic enzymes enable low-temperature biocatalysis, but remain underexplored in Antarctic actinomycetes. Here, we report the discovery and first-step characterization of a CALB-like cold-active lipolytic enzyme (PanLip) from Pseudonocardia antarctica. Sequence and structure analyses revealed a canonical alpha/beta-hydrolase fold with a conserved Ser-Asp-His triad and short helical elements around the pocket reminiscent of CALB's alpha 5/alpha 10 lid. Mature PanLip was expressed primarily as inclusion bodies in E. coli; an N-terminally truncation (PanLip Delta N) improved solubility and PanLip Delta N was purified by Ni-NTA. Far-UV CD confirmed a folded alpha/beta architecture. PanLip Delta N favored short-chain substrates (p-NPA, kcat/KM = 2.4 x 105 M-1<middle dot>s-1) but also showed measurable hydrolytic activity toward natural triglycerides, consistently with a lipase-family esterase. The enzyme showed an activity optimum near 25 degrees C and pH 8.0. The enzyme tolerated low salt (maximal at 0.1 M NaCl), mild glycerol, and selected organic solvents (notably n-hexane), but was inhibited by high salt, Triton X-100, and SDS. AlphaFold predicted high local confidence for the catalytic core; DALI placed PanLip closest to fungal lipases (AFLB/CALB). Temperature-series MD and CABS-flex indicated enhanced surface breathing and flexible segments adjacent to the active site-including a region topologically matching CALB alpha 10-supporting a flexibility-assisted access mechanism at low temperature. Structure-based MSAs did not support a cold adaptation role for the reported VDLPGRS motif. Taken together, these findings position PanLip as a promising cold-active catalyst with CALB-like access control and potential for low-temperature biocatalysis.