Volume 272, Number 1,
Issue of January 3, 1997
pp. 406-413
©1997 by The American Society for Biochemistry and Molecular Biology, Inc.
Characterization of High Affinity Binding between Laminin and the
Acute-phase Protein, Serum Amyloid A
(Received for publication, April 1, 1996, and in revised form, September 10, 1996)
John B.
Ancsin
and
Robert
Kisilevsky
From the Department of Pathology, Queen's University, Syl and
Molly Apps Research Center, Kingston General Hospital, Kingston,
Ontario K7L 3N6, Canada
Serum amyloid A isoforms, apoSAA1 and apoSAA2,
are acute-phase proteins of unknown function and can be precursors of
amyloid AA peptides (AA) found in animal and human amyloid deposits.
These deposits are often a complication of chronic inflammatory
disorders and are associated with a local disturbance in basement
membrane (BM). In the course of trying to understand the pathogenesis
of this disease laminin, a major BM glycoprotein, has been discovered to bind saturably, and with high affinity to murine acute-phase apoSAA.
This interaction involves a single class of binding sites, which are
ionic in nature, conformation-dependent, and possibly involve sulfhydryls. Binding activity was significantly enhanced by
Zn2+, an effect possibly mediated through Cys-rich zinc
finger-like sequences on laminin. Collagen type IV also bound apoSAA
but with lower affinity. Unexpectedly, no binding was detected for
perlecan, a BM proteoglycan previously implicated in AA
fibrillogenesis, although a low affinity interaction cannot be
excluded. Entactin, another BM protein that functions to cross-link the
BM matrix and is normally complexed with laminin, could inhibit
laminin-apoSAA binding suggesting apoSAA does not bind to normal BM.
Since laminin binds apoSAA with high affinity and has previously been
shown to codeposit with AA amyloid fibrils, we postulate that laminin interacts with apoSAA and facilitates nucleation events leading to
fibrillogenesis. This work also provides further support for the
hypothesis that a disturbance in BM metabolism contributes to the
genesis of amyloid. The specificity and avidity of the laminin-apoSAA
interaction also implies that it may be a normal event occurring during
the inflammatory process, which mediates one or more of the functions
recently proposed for apoSAA.