The “Linker” Region (Amino Acids 38-47) of the Disintegrin Elegantin Is a Novel Inhibitory Domain of Integrin α5β1-Dependent Cell Adhesion on Fibronectin

Structural Insight into Integrin Recognition and Anticancer Activity of Echistatin

Echistatin (Ech) is a short disintegrin with a long ⁴²NPHKGPAT C-terminal tail. We determined the 3-D structure of Ech by X-ray crystallography. Superimposition of the structures of chains A and B showed conformational differences in their RGD loops and C-termini. The chain A structure is consistent with our NMR analysis that the GPAT residues of the C-terminus cannot be observed due to high flexibility. The hydrogen bond patterns of the RGD loop and between the RGD loop and C-terminus in Ech were the same as those of the corresponding residues in medium disintegrins. The mutant with C-terminal HKGPAT truncation caused 6.4-, 7.0-, 11.7-, and 18.6-fold decreases in inhibiting integrins αvβ3, αIIbβ3, αvβ5, and α5β1. Mutagenesis of the C-terminus showed that the H44A mutant caused 2.5- and 4.4-fold increases in inhibiting αIIbβ3 and α5β1, and the K45A mutant caused a 2.6-fold decrease in inhibiting αIIbβ3. We found that Ech inhibited VEGF-induced HUVEC proliferation with an IC₅₀ value of 103.2 nM and inhibited the migration of A375, U373MG, and Panc-1 tumor cells with IC₅₀ values of 1.5, 5.7, and 154.5 nM. These findings suggest that Ech is a potential anticancer agent, and its C-terminal region can be optimized to improve its anticancer activity.

Expression in Pichia pastoris and characterization of echistatin, an RGD-containing short disintegrin

Echistatin (Ech) is a potent inhibitor of integrins and was isolated from snake Echis carinatus. To facilitate the study on the molecular determinants of integrin-ligand interactions, we expressed recombinant Ech and its mutants in the Pichia pastoris (P. pastoris) expression system and purified them to homogeneity with the yields of 2-7 mg/L. Ech produced in P. pastoris inhibited platelet aggregation with the IC(50) value of 210.5 nM. The sequential assignment and structure analysis of recombinant Ech were obtained by 2D and 3D (15)N-edited NMR spectra. These data suggests that Ech produced in P. pastoris retained its function and native fold. The results presented here provide the evidences that four disulfide-bonded peptide inhibitor of integrin, Ech, can be expressed in P. pastoris with correct fold and high yield. Platelet aggregation analysis of Ech mutants showed that the length of C-terminus and the K45 residue of Ech are important for interacting with integrin αIIbβ3. We also found that recombinant Ech can inhibit the migration of human A375 melanoma cell. These findings may serve as the basis for understanding the activities of Ech.