Reevaluation of the hydrophobic nature of the 110-kD calmodulin-, actin-, and membrane-binding protein of the intestinal microvillus

✍ Scribed by Karen A. Conzelman; Mark S. Mooseker

• Publisher: John Wiley and Sons
• Year: 1986
• Tongue: English
• Weight: 614 KB
• Volume: 30
• Category: Article
• ISSN: 0730-2312
• DOI: 10.1002/jcb.240300308

✦ Synopsis

A complex of calmodulin (CM) and the 110-kD (llOK) subunit composes the helical array of cross-bridges linking the microvillus actin filament bundle with the membrane. The hydrophobic properties of the llOK protein, assessed by the detergent phase partitioning assay [Bordier C: J Biol Chem 256:1604, 19811, are highly dependent on the solution conditions used in its isolation. The ATPdissociable 11OK-CM complex [Howe and Mooseker: J Cell Biol 9797'4, 19831 exhibits hydrophilic characteristics in this assay. In contrast, the 110K subunit extracted from brush borders by Triton X-100, sodium dodecyl sulfate, and sodium pyrophosphate (detergent-treated l10K) [Glenney JR, Glenney P: Cell 37:743, 19841 behaves as a hydrophobic protein. However, because the soluble hydrophilic 110K-CM can be rendered hydrophobic by treating the complex with the same detergent and salt conditions used in the preparation of detergent-treated llOK, the properties of detergent-treated llOK seem likely to be an effect of the solution conditions on its native conformation, sedimentability, or exposure of binding domains. In addition, the detergent-treated 110K is devoid of calmodulin and no longer exhibits the actin-binding activity characteristic of the ATP-dissociable 11OK-CM and of the intact complex in situ. With two partially purified preparations of the 110K subunit exhibiting such dramatically distinct properties, it seems premature to define the nature of the llOK subunit's association with the membrane at this time.