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J. Virol., 01 1998, 358-365, Vol 72, No. 1
SA Hogenhout, F van der Wilk, M Verbeek, RW Goldbach and JF van den Heuvel
A GroEL homolog with a molecular mass of 60 kDa, produced by the primary
endosymbiotic bacterium (a Buchnera sp.) of Myzus persicae and released
into the hemolymph, has previously been shown to be a key protein in the
transmission of potato leafroll virus (PLRV). Like other luteoviruses and
pea enation mosaic virus, PLRV readily binds to extracellular Buchnera
GroEL, and in vivo interference in this interaction coincides with reduced
capsid integrity and loss of infectivity. To gain more knowledge of the
nature of the association between PLRV and Buchnera GroEL, the groE operon
of the primary endosymbiont of M. persicae (MpB groE) and its flanking
sequences were characterized and the PLRV-binding domain of Buchnera GroEL
was identified by deletion mutant analysis. MpB GroEL has extensive
sequence similarity (92%) with Escherichia coli GroEL and other members of
the chaperonin-60 family. The genomic organization of the Buchnera groE
operon is similar to that of the groE operon of E. coli except that a
constitutive promoter sequence could not be identified; only the heat shock
promoter was present. By a virus overlay assay of protein blots, it was
shown that purified PLRV bound as efficiently to recombinant MpB GroEL
(expressed in E. coli) as it did to wild-type MpB GroEL. Mutational
analysis of the gene encoding MpB GroEL revealed that the PLRV-binding site
was located in the so-called equatorial domain and not in the apical domain
which is generally involved in polypeptide binding and folding. Buchnera
GroEL mutants lacking the entire equatorial domain or parts of it lost the
ability to bind PLRV. The equatorial domain is made up of two regions at
the N and C termini that are not contiguous in the amino acid sequence but
are in spatial proximity after folding of the GroEL polypeptide. Both the
N- and C- terminal regions of the equatorial domain were implicated in
virus binding.
Copyright © 1998, American Society for Microbiology
Potato leafroll virus binds to the equatorial domain of the aphid endosymbiotic GroEL homolog
Department of Virology, DLO Research Institute for Plant Protection, Wageningen, The Netherlands.
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