Modulation of Ligand binding by alternative splicing of the αPS2 integrin subunit

• Published in: Journal of cellular biochemistry Vol. 102; no. 1; pp. 211 - 223
• Main Authors: Bunch, Thomas A., Kendall, Timmy L., Shakalya, Kishore, Mahadevan, Daruka, Brower, Danny L.
• Format: Journal Article
• Language: English
• Published: Hoboken Wiley Subscription Services, Inc., A Wiley Company 01.09.2007
• Subjects: cell adhesion; integrin alternative splicing; integrin structure-function; integrin α7
• ISSN: 0730-2312; 1097-4644
• DOI: 10.1002/jcb.21288

The Drosophila αPS2 integrin subunit is found in two isoforms. αPS2C contains 25 residues not found in αPS2m8, encoded by the alternative eighth exon. Previously, it was shown that cells expressing αPS2C spread more effectively than αPS2m8 cells on fragments of the ECM protein Tiggrin, and that αPS2C‐containing integrins are relatively insensitive to depletion of Ca2+. Using a ligand mimetic probe for Tiggrin affinity (TWOW‐1), we show that the affinity of αPS2CβPS for this ligand is much higher than that of αPS2m8βPS. However, the two isoforms become more similar in the presence of activating levels of Mn2+. Modeling indicates that the exon 8‐encoded residues replace the third β strand of the third blade of the α subunit β‐propeller structure, and generate an exaggerated loop between this and the fourth strand. αPS2 subunits with the extra loop structure but with an m8‐like third strand, or subunits with a C‐like strand but an m8‐like short loop, both fail to show αPS2C‐like affinity for TWOW‐1. Surprisingly, a single C > m8‐like change at the third strand‐loop transition point is sufficient to make αPS2C require Ca2+ for function, despite the absence of any known cation binding site in this region. These data indicate that alternative splicing in integrin α subunit extracellular domains may affect ligand affinity via relatively subtle alterations in integrin conformation. These results may have relevance for vertebrate α6 and α7, which are alternatively spliced at the same site. J. Cell. Biochem. 102: 211–223, 2007. © 2007 Wiley‐Liss, Inc.