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proline-rich proteins?

Tue Nov 2 11:55:03 EST 1993

On Tue, 2 Nov 93 16:24:07 +0900, Los Dmitry Anatolievitch 
<losda at nibb.ac.jp> writes:

> Hello netters,
> Could somebody tell me what is the role(s) of proline-rich
> proteins in plants and bacteria. Any examples?

There are several classes of proline-rich proteins in plants, and 
these appear to be components of the plant extracellular matrix.  
Some recent reviews covering classes of cell wall proteins, including 
proline-rich proteins include:

Carpita, N.C., and Gibeaut, D.M.  1993.  The Plant Journal 3, 1-30.
Keller, B.  1993.  Plant Physiology 101, 1127-1130.
Showalter, A.M.  1993.  Plant Cell 5, 9-23.

Two classes of proline-rich proteins include hydroxy-proline rich 
glycoproteins (HRGPs) and repetitive proline-rich proteins (RPRPs).  
In HRGPs, most of the prolines are post-translationally hydroxylated 
and the proteins are abundantly glycosylated.  In RPRPs, about half 
of the proline residues are hydroxylated, and the proteins are only 
lightly glycosylated, if at all.  However, recent work by Kileszewski 
et al. (1992.  Plant Physiol. 98, 919-926) indicates that the 
dicotomy between these two classes is blurred, since some proteins 
may contain motifs characteristic of both classes. 

Several roles have been proposed for proline-rich proteins.  
They can become covalently cross-linked into the cell wall 
during development, and may increase wall strength.  This cross-
linking can also occur rapidly in response to elicitors  (Bradley et 
al., 1992. Cell 70, 21-30).  Perhaps they can form a barrier 
to pathogen ingress?  Also, because they occur in secondary walls that 
contain lignin, they may serve as a scaffold for lignin deposition 
(Ye et al., 1991.  Plant Journal 1, 175-183).  In my lab, we have 
also observed that PRPs are detectable in Casparian strips, and may 
therefore be related to suberin deposition, as well (unpublished 
observation so far).

We have seen that several antibodies against PRPs cross-react with 
two peptides on the cell surface of the gram negative bacterium, 
Rhizobium.  Therefore, I would also be interested to learn of PRP-
like proteins known from bacteria.

Kate VandenBosch
Department of Biology
Texas A & M University
kate at bio.tamu.edu

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