Characterization of the gila monster (Heloderma suspectum suspectum) venom proteome

The archetypical venomous lizard species are the helodermatids, the gila monsters (Heloderma suspectum) and the beaded lizards (Heloderma horridum). In the present study, the gila monster venom proteome was characterized using 2D-gel electrophoresis and tandem mass spectrometry-based de novo peptide sequencing followed by protein identification based on sequence homology. A total of 39 different proteins were identified out of the 58 selected spots that represent the major constituents of venom. Of these proteins, 19 have not previously been identified in helodermatid venom. The data showed that helodermatid venom is complex and that this complexity is caused by genetic isoforms and post-translational modifications including proteolytic processing. In addition, the venom proteome analysis revealed that the major constituents of the gila monster venom are kallikrein-like serine proteinases (EC 3.4.21) and phospholipase A2 (type III) enzymes (EC 3.1.1.4). A neuroendocrine convertase 1 homolog that most likely converts the proforms of the previously identified bioactive exendins into the mature and active forms was identified suggesting that these peptide toxins are secreted as proforms that are activated by proteolytic cleavage following secretion as opposed to being activated intracellularly. The presented global protein identification-analysis provides the first overview of the helodermatid venom composition.

Biological significance: The helodermatid lizards are the classical venomous lizards, and the pharmacological potential of the venom from these species has been known for years; best illustrated by the identification of exendin-4, which is now used in the treatment of type 2 diabetes. Despite the potential, no global analyses of the protein components in the venom exist. A hindrance is the lack of a genome sequence because it prevents protein identification using a conventional approach where MS data are searched against predicted protein sequences based on the genome sequence. However, in the recent years the development of software tools for de novo sequencing and homology searches have improved significantly facilitating the first global analysis of the major protein components of helodermatid venom presented in this study. We have used a 2D-gel approach and determined the protein components in the 58 major spots resulting in the identification of 39 unique proteins. Of these, 19 have not previously been identified in helodermatid venom. The analysis provides results with impact on our understanding of the function and evolution of venom proteins, and serves as a basis for further unraveling of the pharmaceutical potential of the venom components.