Impact of Propeptide Cleavage on the Stability and Activity of a Streptococcal Immunomodulatory C5a Peptidase for Biopharmaceutical Development.

Posttranslational modifications of proteins can impact their therapeutic efficacy, stability, and potential for pharmaceutical development. The Group AC5a peptidase (ScpA) is a multi-domain protein composed of an N-terminal signal peptide, a catalytic domain (including propeptide), three fibronectin domains, and cell membrane-associated domains. It is one of several proteins produced by Group Aknown to cleave components of the human complement system. After signal peptide removal, ScpA undergoes autoproteolysis and cleaves its propeptide for full maturation. The exact location and mechanism of the propeptide cleavage, and the impact of this cleavage on stability and activity, are not clearly understood, and the exact primary sequence of the final enzyme is not known. A form of ScpA with no autoproteolysis fragments of propeptide present may be more desirable for pharmaceutical development from a regulatory and a biocompatibility in the body perspective. The current study describes an in-depth structural and functional characterization of propeptide truncated variants of ScpA expressed incells. All three purified ScpA variants, ScpA, 79ΔPro, and 92ΔPro, starting with N32, D79, and A92 positions, respectively, showed similar activity against C5a, which suggests a propeptide-independent activity profile of ScpA. CE-SDS and MALDI top-down sequencing analyses highlight a time-dependent propeptide autoproteolysis of ScpA at 37 °C with a distinct end point at A92 and/or D93. In comparison, all three variants of ScpA exhibit similar stability, melting temperatures, and secondary structure orientation. In summary, this work not only highlights propeptide localization but also provides a strategy to recombinantly produce a final mature and active form of ScpA without any propeptide-related fragments.