Functional analysis of four single (RGDWL, RGDWM, RGDWP, RGDMN) and two double (RGDNM, RGDMP) mutants: The importance of methionine (M) in the functional potency of recombinant mojastin (r-Moj)

Structural and Functional Differences of Rhodostomin and Echistatin in Integrin Recognition and Biological Implications

Rhodostomin (Rho) and Echistatin (Ech) are RGD-containing disintegrins with different sizes, disulfide bond patterns, and amino acid sequences in their RGD loops and C-termini. Cell adhesion analyzes showed that Rho exhibited a 5.2-, 18.9-, 2.2-, and 1.7-fold lower inhibitory activity against integrins αvβ3, α5β1, αIIbβ3, and αvβ5 in comparison with those of Ech. In contrast, Rho exhibited an 8.8-fold higher activity than Ech in inhibiting integrin αvβ6. The swapping of Ech's RGD loop and C-terminal sequences into those of Rho cannot increase its integrins' inhibitory activities. Interestingly, the mutation of Ech into Rho's RGD loop PRGDMP sequence and C-terminal YH sequence caused an 8.2-fold higher activity in inhibiting integrin αvβ6. Structural analyzes of Rho and Ech showed that they have similar conformations in their RGD loop and different conformations in their C-terminal regions. Molecular docking found that not only the RGD loop but also the C-terminal region of Rho and Ech interacted with integrins, showing that the C-terminal region is also important for integrin recognition. The docking of Rho into integrin αvβ6 showed that the C-terminal H68 residue of Rho interacted with D129 of β6. In contrast, the docking of Ech into integrin α5β1 showed that the C-terminal H44 residue of Ech interacted with Q191 of β1. Ech exhibited 78.5- and 10.9-fold higher activities in inhibiting HUVEC proliferation and A375 melanoma cell migration than those of Rho. These findings demonstrate that the disulfide bond pattern, RGD loop, and C-terminal region of disintegrins may cause their functional differences. The functional and structural differences between Rho and Ech support their potential as scaffolds to design drugs targeting their respective integrins.

Recombinant and Chimeric Disintegrins in Preclinical Research

Disintegrins are a family of small cysteine-rich peptides, found in a wide variety of snake venoms of different phylogenetic origin. These peptides selectively bind to integrins, which are heterodimeric adhesion receptors that play a fundamental role in the regulation of many physiological and pathological processes, such as hemostasis and tumor metastasis. Most disintegrins interact with integrins through the RGD (Arg-Gly-Asp) sequence loop, resulting in an active site that modulates the integrin activity. Some variations in the tripeptide sequence and the variability in its neighborhood result in a different specificity or affinity toward integrin receptors from platelets, tumor cells or neutrophils. Recombinant forms of these proteins are obtained mainly through Escherichia coli, which is the most common host used for heterologous expression. Advances in the study of the structure-activity relationship and importance of some regions of the molecule, especially the hairpin loop and the C-terminus, rely on approaches such as site-directed mutagenesis and the design and expression of chimeric peptides. This review provides highlights of the biological relevance and contribution of recombinant disintegrins to the understanding of their binding specificity, biological activities and therapeutic potential. The biological and pharmacological relevance on the newest discoveries about this family of integrin-binding proteins are discussed.