Proteinase pattern of honeybee prepupae from healthy and American Foulbrood infected bees investigated by zymography

Proteomic insight into the interaction of Paenibacillus larvae with honey bee larvae before capping collected from an American foulbrood outbreak: Pathogen proteins within the host, lysis signatures and interaction markers

American foulbrood (AFB) is a devastating disease of honey bees. There remains a gap in the understanding of the interactions between the causative agent and host, so we used shotgun proteomics to gain new insights. Nano-LC-MS/MS analysis preceded visual description and Paenibacillus larvae identification in the same individual sample. A further critical part of our methodology was that larvae before capping were used as the model stage. The identification of the virulence factors SplA, PlCBP49, enolase, and DnaK in all P. larvae-positive samples was consistent with previous studies. Furthermore, the results were consistent with the array of virulence factors identified in an in vitro study of P. larvae exoprotein fractions. Although an S-layer protein and a putative bacteriocin were highlighted as important, the microbial collagenase ColA and InhA were not found in our samples. The most important virulence factor identified was isoform of neutral metalloproteinase (UniProt: V9WB82), a major protein marker responsible for the shift in the PCA biplot. This protein is associated with larval decay and together with other virulence factors (bacteriocin) can play a key role in protection against secondary invaders. Overall, this study provides new knowledge on host-pathogen interactions and a new methodical approach to study the disease.

Detection and pH-Thermal Characterization of Proteinases Exclusive of Honeybee Worker-Fate Larvae (Apis mellifera L.)

The occurrence of the honeybee caste polyphenism arises when a change in diet is transduced into cellular metabolic responses, resulting in a developmental shift mediated by gene expression. The aim of this investigation was to detect and describe the expression profile of water-soluble proteases during the ontogenesis of honeybee worker-fate larvae. The extraction of insect homogenates was followed by the electrophoretic separation of the protein extract in polyacrylamide gels under semi-denaturing condition, precast with gelatin, pollen, or royal jelly protein extracts. The worker-fate honeybee larva showed a proteolytic pattern that varied with aging, and a protease with the highest activity at 72 h after hatching was named PS4. PS4 has a molecular weight of 45 kDa, it remained active until cell sealing, and its enzymatic properties suggest a serine-proteinase nature. To define the process that originates a queen-fate larvae, royal jelly and pollen were analysed, but PS4 was not detected in either of them. The effect of food on the PS4 was investigated by mixing crude extracts of queen and worker-fate larvae with pollen and royal jelly, respectively. Only royal jelly inhibited PS4 in worker-fate larvae. Taken together, our data suggest that PS4 could be involved in caste differentiation.

Structural and functional relationship of Cassia obtusifolia trypsin inhibitor to understand its digestive resistance against Pieris rapae

Although digestive resistance of Kunitz protease inhibitors has been reported extensively, the molecular mechanism is not well established. In the present study, the first X-ray structure of Cassia obtusifolia trypsin inhibitor (COTI), a member of Kunitz protease inhibitors, was solved at a resolution of 1.9 Å. The structure adopted a classic β-trefoil fold with the inhibitory loop protruding from the hydrophobic core. The role of Phe139, a unique residue in Kunitz protease inhibitors, and Arg63 in the COTI structure was verified by F139A and R63E mutants. COTI was a specific inhibitor of bovine trypsin and the result was also verified by COTI-trypsin complex formation. Meanwhile, COTI showed equivalent inhibitory activity with that of soybean trypsin inhibitor against bovine trypsin and midgut trypsin from Pieris rapae. The F139 and R63E mutants further indicated that inhibitory specificity and efficiency of COTI were closely related to the global framework, the conformation and the amino acid composition of reactive loop. Finally, a midgut trypsin from P. rapae (PrSP40), which might be involve in the food digestion, was proposed to be a potential target of COTI and might be a promising target for future crop-protection strategy. The results supported the digestive resistance of COTI.