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1994-09-19
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Document 0465
DOCN M9490465
TI Pepstatin A: polymerization of an oligopeptide.
DT 9411
AU Mothes E; Shoeman RL; Traub P; Max-Planck-Institut fur Zellbiologie,
Ladenburg, Germany.
SO Micron. 1994;25(2):189-217. Unique Identifier : AIDSLINE MED/94332557
AB Pepstatin A, a pentapeptide with the molecular weight of 686, is a
naturally occurring inhibitor of aspartyl proteases secreted by
Streptomyces species. Above a critical concentration of 0.1 mM at low
ionic strength and neutral pH, it can polymerize into filaments which
may extend over several micrometers. After negative staining, these
filaments show a helical substructure with characteristic diameters
ranging from 6 to 12 nm. Selected images at higher magnification suggest
the filaments are composed of two intertwined 6 nm strands. This is in
agreement with the optical diffraction analysis which additionally
established a periodic pitch of 25 nm for the helical intertwining.
Rotary shadowing of the pepstatin A filaments clearly demonstrated the
right-handedness of the helical twist. In physiological salt solution or
at higher concentrations of pepstatin A, a variety of higher order
structures were observed, including ribbons, sheets and cylinders with
both regular and twisted or irregular geometries. Pepstatin A can
interact with intermediate filament subunit proteins. These proteins
possess a long, alpha-helical rod domain that forms coiled-coil dimers,
which through both hydrophobic and ionic interactions form tetramers
which, in turn, in the presence of physiological salt concentrations,
polymerize into the 10 nm intermediate filaments. In the absence of
salt, pepstatin A and intermediate filament proteins polymerize into
long filaments with a rough surface and a diameter of 15-17 nm. This
polymerization appears to be primarily driven by nonionic interactions
between pepstatin A and polymerization-competent forms of intermediate
filament proteins, resulting in a composite filament.
Polymerization-incompetent proteolytic fragments of vimentin, lacking
portions of the head and/or tail domain, failed to copolymerize with
pepstatin A into long filaments under these conditions. These peptides,
as well as bovine serum albumin, were found to stick to the surface of
pepstatin A filaments, ribbons and sheets. Independent evidence for
direct association of pepstatin A with intermediate filament subunit
proteins was provided not only by electron microscopy but also by UV
difference spectra. Pepstatin A loses its ability to inhibit the
aspartyl protease of the human immunodeficiency virus type 1 following
polymerization into the higher order structures described here. The
amazing fact that pepstatin A can spontaneously self-associate to form
very large polymers seems to be a more rare event for such small
peptides. The other examples of synthetic or naturally occurring
oligopeptides discussed in this review which are able to polymerize into
higher order structures possess a common property, their hydrophobicity,
often manifested by clusters of valine or isoleucine residues.(ABSTRACT
TRUNCATED AT 400 WORDS)
DE Comparative Study Intermediate Filament Proteins/*METABOLISM
Microscopy, Electron Pepstatins/CHEMISTRY/*METABOLISM
Polymers/*METABOLISM JOURNAL ARTICLE REVIEW REVIEW, TUTORIAL
SOURCE: National Library of Medicine. NOTICE: This material may be
protected by Copyright Law (Title 17, U.S.Code).