Di-methylation of a specific arginine in AAV5 capsid proteins

We have identified significant arginine di-methylation (> 40 %) on a specific arginine in AAV5 capsid proteins derived from insect cell (SF9) based systems. We have examined the capsid proteins derived from the same AAV5 serotype transgene vector construct produced using a HEK293 host cell production system and observe some, but about 10 fold less relative abundance of di-methylation on the same arginine of the capsid proteins produced with that system. This suggests there may be a relative difference in one or more aspects of post-translational di-methylation proclivity for this same site on the same protein between these two expression platforms. We also examined AAV9 serotype capsid proteins from the same two AAV production systems and observe no arginine di-methylation and/or arginine mono-methylation on any of the arginines in the capsid proteins from either. This short communication outlines details of these observations and why they may be of interest from several different perspectives.