Affiliation:
1. Department of Molecular Cell Biology, Microbiology and Institute for Molecular Biology, State University of Utrecht, Padualaan 8, Utrecht, The Netherlands
2. Electron Microscopy Sections, and Institute for Molecular Biology, State University of Utrecht, Padualaan 8, Utrecht, The Netherlands
Abstract
In a previous paper (A. Verkleij, L. van Alphen, J. Bijvelt, and B. Lugtenberg, Biochim. Biophys. Acta
466:
269-282, 1977) we have hypothesized that particles on the outer fracture face of the outer membrane ([Formula: see text]), with corresponding pits on the inner fracture face of the outer membrane ([Formula: see text]), consist of lipopolysaccharide (LPS) aggregates stabilized by divalent cations and that they might contain protein and/or phospholipid. In the present paper the roles of LPS, cations, and proteins in these [Formula: see text] particles are described more extensively, using a strain that lacks the major outer membrane proteins, b, c, and d (b
−
c
−
d
−
), and has a reduction in the number of [Formula: see text] particles of 75%. To study the role of divalent cations in the formation of [Formula: see text] particles, these b
−
c
−
d
−
cells were grown or incubated with Ca
2+
, Mg
2+
, or putrescine. The presence of Ca
2+
resulted in the appearance of many [Formula: see text] particles and [Formula: see text] pits. Mg
2+
and putrescine were less effective than Ca
2+
. Introduction of these particles was not accompanied by alterations in the relative amounts of LPS and cell envelope proteins. Ca
2+
treatment of a heptoseless derivative of a b
−
c
−
d
−
strain did not result in morphological changes. Incubation of Ca
2+
-treated cells with ethylenediaminetetraacetate caused the disappearance of the introduced particles as well as the release of more than 60% of the cellular LPS. These results strongly support the hypothesis that LPS is involved in the formation of [Formula: see text] particles and [Formula: see text] pits. The roles of various outer membrane proteins in the formation of [Formula: see text] particles were studied by comparing the freeze-fracture morphology of b
−
c
−
d
−
cells with that of cells which contain one of the outer membrane proteins b, c, d, and e or the receptor protein for bacteriophage lambda. The results showed that the presence of any of these five proteins in a b
−
c
−
d
−
background resulted in a large increase in the number of [Formula: see text] particles and [Formula: see text] pits, indicating that these proteins are, independent of each other, involved in the formation of [Formula: see text] particles and [Formula: see text] pits. The simplest explanation for the results is that in wild-type cells each particle consists of LPS complexed with some molecules of a single protein species, stabilized by either divalent cations or polyamines. It is hypothesized that the outer membrane of the wild-type cell contains a heterogeneous population of particles, of which 75% consists of protein b-LPS, protein c-LPS, and protein d-LPS particles. A function of these particles as aqueous pores is proposed.
Publisher
American Society for Microbiology
Subject
Molecular Biology,Microbiology
Cited by
77 articles.
订阅此论文施引文献
订阅此论文施引文献,注册后可以免费订阅5篇论文的施引文献,订阅后可以查看论文全部施引文献