Purification and Characterization of Ovotransferrin from Crocodylus siamensis

Analysis of Siamese Crocodile (Crocodylus siamensis) Eggshell Proteome

The proteins and pigment of the eggshell of the Siamese crocodile (Crocodylus siamensis) were analysed. For proteomic analysis, various decalcification methods were used when the two main surface layers were analyzed. These layers are important for antimicrobial defense of egg (particularly the cuticle). We found 58 proteins in both layers, of which 4 were specific for the cuticle and 26 for the palisade (honeycomb) layer. Substantial differences between proteins in the eggshell of crocodile and previously described birds' eggshells exist (both in terms of quality and quantity), however, the entire proteome of Crocodilians has not been described yet. The most abundant protein was thyroglobulin. The role of determined proteins in the eggshell of the Siamese crocodile is discussed. For the first time, the presence of porphyrin pigment is reported in a crocodilian eggshell, albeit in a small amount (about 2 to 3 orders of magnitude lower than white avian eggs).

Purification, characterization, cloning and structural analysis of Crocodylus siamensis ovotransferrin for insight into functions of iron binding and autocleavage

Ovotransferrin (OTf), the major protein constituent of egg white, is of great interest due to its pivotal role in biological iron transport and storage processes and its spontaneous autocleavage into peptidic fragments with alternative biological properties, such as antibacterial and antioxidant activities. However, despite being well-investigated in avian, a detailed elucidation of the structure-function relationship of ovotransferrins in the closely related order of Crocodilia has not been reported to date. In this study, electron paramagnetic resonance (EPR) confirmed the presence of two spectroscopically distinct ferric iron binding sites in Crocodylus siamensis OTf (cOTf), but implied a five-fold lower quantity of bound iron than in hen OTf (hOTf). In addition, quantitative estimation of free sulfhydryl groups revealed slight differences to hOTf. To gain a better structural understanding of cOTf, we found a cOTf gene consisting of an open reading frame of 2040bp and encoding a protein of 679 amino acids. In silico prediction of the three-dimensional structure of cOTf and comparison with hOTf revealed four evolutionarily conserved iron-binding sites in both N- and C-lobes, as well as the presence of only 13 of the 15 disulfide bonds in hOTf. This evolutionary loss of disulfide linkages in conjunction with the lack of hydrogen bonding from a dilysine trigger in the C-lobe are presumed to affect the iron binding and autocleavage character of cOTf. As a result, cOTf may be capable of exerting a more diverse array of functions compared to its avian counterparts; for instance, ion buffering, antioxidant and antimicrobial activities.

Antimicrobial effects of novel peptides cOT2 and sOT2 derived from Crocodylus siamensis and Pelodiscus sinensis ovotransferrins

In light of the increasing threat of bacterial drug resistance to human health on a global scale, research and development of antimicrobial peptides as a novel class of potent antibiotics has gained considerable attention. The present study focuses on the structural evaluation and membrane interaction of two new cationic antimicrobial peptides, cOT2 and sOT2, derived from Siamese crocodile (Crocodylus siamensis) and Chinese softshell turtle (Pelodiscus sinensis) ovotransferrins. Here, cOT1 (+3) and sOT1 (+3) were derived from reptile ovotransferrins by chromatographic purification and characterized by mass spectrometry and N-terminal sequencing analysis. In order to increase the antimicrobial efficacy, two novel peptides, cOT2 (+6) and sOT2 (+5), were designed and synthesized as "naturally-engineered" by primary amino acid sequence extension of cOT1 and sOT1, respectively. These rational designs of modified peptides were assayed in term of antimicrobial activity. These peptides display strong antimicrobial activity against several bacterial strains, e.g. Vibrio cholerae, Bacillus megaterium, and Bacillus pumilus TISTR 905, with MICs of 7-16.1μM. In terms of structural conformation in mimic environments, CD spectroscopic analysis of the secondary peptides structure features revealed fairly the similarity on α-helical content with magainin II. Hence, the modes of actions have been speculated as toroidal and carpet model. Furthermore, the disruption of intact bacterial cells induced by cOT2 and sOT2 was investigated by SEM and AFM. The results provided evidence that cOT2 and sOT2 have the potential to cause different morphological changes of bacterial cells and that these effects can be enhanced by increasing the peptide concentration.