Am. J. Respir. Cell Mol. Biol., Vol 11, No. 6, 12 1994, 692-700.
Interaction of surfactant protein A with cellular myosin
D Michelis, MZ Kounnas, WS Argraves, ED Sanford, JD Borchelt and JR Wright
Department of Physiology, University of California, San Francisco.
The goal of the current investigation was to characterize, purify, and
identify the proteins that bind surfactant protein A (SP-A). Several
polypeptides were purified by SP-A affinity chromatography, and the 200 kD
major polypeptide that reacted with SP-A on ligand blots was purified
further by preparative SDS-PAGE. Protein sequencing of proteolytically
derived subfragments of this polypeptide gave sequences that corresponded
completely with nonmuscle (cellular) myosin heavy chain. The 200 kD
polypeptide was then found to be immunoreactive with antibodies against
cellular myosin. A smaller polypeptide of 135 kD also binds SP-A and
appears to be a proteolytic fragment of the 200 kD peptide. The ability of
SP-A to bind myosin was confirmed in a microtiter well assay and was found
to be concentration dependent. We speculated that the physiologic relevance
of the interaction of SP-A with myosin might be to facilitate clearance of
myosin from the alveolar subphase following its release during lung injury.
In support of this hypothesis, we found that there were detectable levels
of myosin in lavage fluid and that SP-A could indeed enhance uptake and
degradation of myosin by alveolar macrophages.
