LAP, an alcohol acetaldehyde dehydrogenase enzyme in Listeria, promotes bacterial adhesion to enterocyte-like Caco-2 cells only in pathogenic species

Abstract

Listeriaadhesion protein (LAP), an alcohol acetaldehyde dehydrogenase (lmo1634), interacts with host-cell receptor Hsp60 to promote bacterial adhesion during the intestinal phase ofListeria monocytogenesinfection. The LAP homologue is present in pathogens (L. monocytogenes,L. ivanovii) and non-pathogens (L. innocua,L. welshimeri,L. seeligeri); however, its role in non-pathogens is unknown. Sequence analysis revealed 98 % amino acid similarity in LAP from allListeriaspecies. The N-terminus contains acetaldehyde dehydrogenase (ALDH) and the C-terminus an alcohol dehydrogenase (ADH). Recombinant LAP fromL. monocytogenes,L. ivanovii,L. innocuaandL. welshimeriexhibited ALDH and ADH activities, and displayed strong binding affinity (KD2–31 nM) towards Hsp60. Flow cytometry, ELISA and immunoelectron microscopy revealed more surface-associated LAP in pathogens than non-pathogens. Pathogens exhibited significantly higher adhesion (P<0.05) to Caco-2 cells than non-pathogens; however, pretreatment of bacteria with Hsp60 caused 47–92 % reduction in adhesion only in pathogens. These data suggest that biochemical properties of LAP from pathogenicListeriaare similar to those of the protein from non-pathogens in many respects, such as substrate specificity, immunogenicity, and binding affinity to Hsp60. However, protein fractionation analysis of extracts from pathogenic and non-pathogenicListeriaspecies revealed that LAP was greatly reduced in intracellular and cell-surface protein fractions, and undetectable in the extracellular milieu of non-pathogens even though thelaptranscript levels were similar for both. Furthermore, a LAP preparation fromL. monocytogenesrestored adhesion in alapmutant (KB208) ofL. monocytogenesbut not inL. innocua, indicating possible lack of surface reassociation of LAP molecules in this bacterium. Taken together, these data suggest that LAP expression level, cell-surface localization, secretion and reassociation are responsible for LAP-mediated pathogenicity and possibly evolved to adapt to a parasitic life cycle in the host.