Mass spectrometric identification, sequence evolution, and intraspecific variability of dimeric peptides encoded by cockroach akh genes

摘要

Neuropeptides are structurally the most diverse group of messenger molecules of the nervous system. Regarding neuropeptide identification, distribution, function, and evolution, insects are among the best studied invertebrates. Indeed, more than 100 neuropeptides are known from single species. Most of these peptides can easily be identified by direct tissue or cell profiling using MALDI-TOF MS. In these experiments, protein hormones with extensive post-translational modifications such as inter- and intramolecular disulfides are usually missed. It is evident that an exclusion of these bioactive molecules hinders the utilization of direct profiling methods in comprehensive peptidomic analyses. In the current study, we focus on the detection and structural elucidation of homo- and heterodimeric adipokinetic hormone precursor-related peptides (APRPs) of cockroaches. The physiological relevance of these molecules with highly conserved sequences in insects is still uncertain. Sequence similarities with vertebrate growth hormone-releasing factors have been reported, but remarkably, few data regarding APRP processing exist and these data are restricted to locusts. Here, we elucidated sequences of carbamidomethylated APRP monomers of different cockroaches by means of MALDI-TOF MS2, and we were able to identify a surprisingly large number of APRP sequences, resulting either from intraspecific amino acid substitutions within the APRP sequences or C-terminal truncated APRPs.