Structure-Function Relationship of the Disintegrin Family: Sequence Signature and Integrin Interaction

Disintegrins are small cysteine-rich proteins found in a variety of snake venom. These proteins selectively modulate integrin function, heterodimeric receptors involved in cell-cell and cell-matrix interaction that are widely studied as therapeutic targets. Snake venom disintegrins emerged from the snake venom metalloproteinase and are classified according to the sequence size and number of disulfide bonds. Evolutive structure and function diversification of disintegrin family involves a stepwise decrease in the polypeptide chain, loss of cysteine residues, and selectivity. Since the structure elucidation of echistatin, the description of the structural properties of disintegrins has allowed the investigation of the mechanisms involved in integrin-cell-extracellular matrix interaction. This review provides an analysis of the structures of all family groups enabling the description of an expanded classification of the disintegrin family in seven groups. Each group presents a particular disulfide pattern and sequence signatures, facilitating the identification of new disintegrins. The classification was based on the disintegrin-like domain of the human metalloproteinase (ADAM-10). We also present the sequence and structural signatures important for disintegrin-integrin interaction, unveiling the relationship between the structure and function of these proteins.

Functional variability of snake venom metalloproteinases: adaptive advantages in targeting different prey and implications for human envenomation

Snake venom metalloproteinases (SVMPs) are major components in most viperid venoms that induce disturbances in the hemostatic system and tissues of animals envenomated by snakes. These disturbances are involved in human pathology of snake bites and appear to be essential for the capture and digestion of snake's prey and avoidance of predators. SVMPs are a versatile family of venom toxins acting on different hemostatic targets which are present in venoms in distinct structural forms. However, the reason why a large number of different SVMPs are expressed in some venoms is still unclear. In this study, we evaluated the interference of five isolated SVMPs in blood coagulation of humans, birds and small rodents. P-III class SVMPs (fractions Ic, IIb and IIc) possess gelatinolytic and hemorrhagic activities, and, of these, two also show fibrinolytic activity. P-I class SVMPs (fractions IVa and IVb) are only fibrinolytic. P-III class SVMPs reduced clotting time of human plasma. Fraction IIc was characterized as prothrombin activator and fraction Ic as factor X activator. In the absence of Ca²⁺, a firm clot was observed in chicken blood samples with fractions Ic, IIb and partially with fraction IIc. In contrast, without Ca²⁺, only fraction IIc was able to induce a firm clot in rat blood. In conclusion, functionally distinct forms of SVMPs were found in B. neuwiedi venom that affect distinct mechanisms in the coagulation system of humans, birds and small rodents. Distinct SVMPs appear to be more specialized to rat or chicken blood, strengthening the current hypothesis that toxin diversity enhances the possibilities of the snakes for hunting different prey or evading different predators. This functional diversity also impacts the complexity of human envenoming since different hemostatic mechanisms will be targeted by SVMPs accounting for the complexity of the response of humans to venoms.

Label-free quantitative proteomics reveals differentially regulated proteins in the latex of sticky diseased Carica papaya L. plants

Papaya meleira virus (PMeV) is so far the only described laticifer-infecting virus, the causal agent of papaya (Carica papaya L.) sticky disease. The effects of PMeV on the laticifers' regulatory network were addressed here through the proteomic analysis of papaya latex. Using both 1-DE- and 1D-LC-ESI-MS/MS, 160 unique papaya latex proteins were identified, representing 122 new proteins in the latex of this plant. Quantitative analysis by normalized spectral counting revealed 10 down-regulated proteins in the latex of diseased plants, 9 cysteine proteases (chymopapain) and 1 latex serine proteinase inhibitor. A repression of papaya latex proteolytic activity during PMeV infection was hypothesized. This was further confirmed by enzymatic assays that showed a reduction of cysteine-protease-associated proteolytic activity in the diseased papaya latex. These findings are discussed in the context of plant responses against pathogens and may greatly contribute to understand the roles of laticifers in plant stress responses.

Integrin inhibitors from snake venom: exploring the relationship between the structure and activity of RGD-peptides

alphaIIbbeta3 is an integrin that is involved in platelet adhesion and aggregation. This receptor may be inhibited by cysteine-rich peptides known as disintegrins. We isolated two disintegrins from Bothrops jararaca venom called jarastatin and jararacin. We evaluated the structural characteristics and the effects on human platelet aggregation of these disintegrins. Inhibitory profiles were compared to six distinct peptides synthesized based on their RGD hairpin loop primary sequences. Both jarastatin and jararacin inhibited ADP and thrombin induction. Conversely, none of the cyclic peptides showed high-quality activity in assays induced by ADP or thrombin. We constructed homology models for all of these molecules, and theoretically evaluated their interaction with the alphaIIbbeta3 crystal structure using a molecular modeling approach. These results support the observations that the cyclic peptides had little effects, and also reinforce the observation that residues outside the disintegrin RGD sequence are required for interactions with receptor.

Effect of RGD-disintegrins on melanoma cell growth and metastasis: involvement of the actin cytoskeleton, FAK and c-Fos

The effects and molecular mechanisms of RGD-disintegrins isolated from snake venoms on the growth and metastatic potential of B16F10-melanoma cells were investigated. Jarastatin (JT) from Bothrops jararaca is a ligand of alpha(5)beta(1), alpha(v)beta(3) and alpha(m)beta(2) integrins, flavoridin (FL) from Trimeresurus flavoridis binds preferentially to alpha(5)beta(1) and kistrin (KR) from Calloselasma rhodostoma is a selective ligand of alpha(v)beta(3). When injected simultaneously with melanoma cells in mice, the three disintegrins significantly reduced tumor lung colonization. On the other hand, JT and FL, but not KR, inhibited B16F10 cell growth in vitro. Interaction of JT or FL with melanoma cells induced actin cytoskeleton rearrangement, increasing actin polymerization and FAK phosphorylation. The effect of FL correlates with the decrease in the constitutively high nuclear content of c-Fos, whereas JT interfered with NF-kappaB translocation in melanoma cells. None of the disintegrins produced alterations in the nuclear Erk-2. The results provide further evidence to suggest RGD-disintegrins as potent anti-metastatic agents in vivo, and indicate that their interaction with alpha(5)beta(1) integrin interfere with integrin-couple signaling, down-regulating transcription factors and negatively modulating cell proliferation. These effects may contribute to inhibition of melanoma cell invasion in vivo.

Molecular diversity of disintegrin-like domains within metalloproteinase precursors of Bothrops jararaca

Disintegrins are small peptides isolated from the venom of several snake families which act as integrin-antagonists or agonists, interacting with a variety of biological processes mediated by integrins. In this work we describe five new disintegrin-like domains within metalloproteinase precursor sequences, obtained from a Bothrops jararaca venom gland cDNA library. Among the new disintegrin-like domains, four were contained in PIII metalloproteinase precursors, with three of them presenting ECD-motifs and one presenting a new KCD-motif. Moreover, we found three disintegrin-like domains within PII metalloproteinase precursors. Two of them are similar to the already described disintegrins jarastatin and jararacin. The third molecule is unusual, presenting some typical PIII metalloproteinase characteristics but lacking the cysteine-rich domain being, thus, classified as a PII metalloproteinase. Only few reports presented molecules with these characteristics. Sequence analysis suggests that these molecules are intermediate steps between the more ancient PIII and the more recent PII metalloproteinases. We also investigated disintegrin N-terminus diversity in B. jararaca crude venom by purifying jarastatin and jararacin and analyzing them by mass spectrometry.