How do bacteria sense env.?

f0380903 at f0380903 at
Fri Sep 2 10:55:11 EST 1994

In article <3466hh$nd6 at>, kferri at (Karen Ferri) writes:
> Hello all.  Am taking my first micro. class and am absolutely fascinated 
> by it!  I am having a little trouble understanding the mech. by which 
> bacteria sense their environment.  I understand the mech. of chemotaxis; 
> it's how do they sense in the first place I am confused on and haven't 
> been able to find any clear info if at all ( my text omits this).  Some 
> of the terms  the prof used were: omp R, omp C, omp F, sensor in the 
> cytoplasmic membrane and response regulator in the cytoplasm.  Can anyone 
> explain this to me in clear language?  Many thanks, in advance.
> KF

OmpF and OmpC are a type of protein called porins.  They are found in the outer
membrane of E. coli (and other Gram negative bacteria).  Their function is to
form pores or channels in the outer membrane that allow the diffusion of small
molecules (like nutrients) into the periplasmic space (the area between the 
inner and outer membranes).  OmpC is expressed under conditions of increased
osmolarity (more salts in the enviro.) and OmpF is expressed under conditions
of decreased osmolarity.  OmpC and OmpF levels are reciprocal.  That is to say
as more OmpC is expressed there is less OmpF and vice versa.  A protein in the
inner membrane called EnvZ (Env is for envelope; Omp is outer membrane protein)
is the sensor for osmolarity (I don't know what or how EnvZ senses and I don't
know if it is known what the signal is) anyway when EnvZ senses its signal it
can autophosphorylate (A PO4 group is transferred from ATP to EnvZ) EnvZ then
passes the PO4 on to OmpR (which is a cytoplasmic protein despite the name)
OmpR then modulates the expression of OmpC and OmpF.  
A good reference to track down is Bourret, Borkovich and Simon.
Annual Reviews in Biochemistry.  1991.  vol. 60 pp. 401-441.
Hope this helps. :)

Matthew Nilles
f0380903 at
Dept. of Microbiolgy
Washington State University
Pullman, WA

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