Download Another Step Closer to Understanding Plant Cell Wall Biosynthesis

Plant Cell Advance Publication. Published on September 28, 2016, doi:10.1105/tpc.16.00756
IN BRIEF
Another Step Closer to Understanding Plant Cell Wall Biosynthesis: The Crystal Structure of
FUCOSYLTRANSFERASE 1
Plant cell walls consist of cellulose microfibrils
embedded in a matrix of polymers including
hemicelluloses. As one of the main
hemicelluloses in the cell walls of dicots,
xyloglucan is an important target of study to
understand plant cell walls in general and for
polymer applications in biotechnology.
Xyloglucan consists of a β-1,4-linked
backbone of glucosyl residues with or without
sidechains, the most common of which is a
xylosyl residue. The sidechains themselves
can harbor further sidechains, and, ultimately,
24 different sidechains can make up
xyloglucan. Biosynthesis of xyloglucan
(reviewed in Pauly and Keegstra, 2016)
involves members of the glycosyltransferase
(GT)
superfamily
including
a
fucosyltransferase, which was the first plant
cell wall-biosynthetic enzyme discovered. Now,
in a Breakthrough Report from Rocha et al.
(2016),
Arabidopsis
thaliana
FUCOSYLTRANSFERASE 1 (FUT1) provides
the first crystal structure of a plant cell wallbiosynthesis enzyme.
FUT1 transfers fucose from the donor
GDP-fucose to galatosyl residues on
xyloglucan and is a member of
glycosyltransferase family 37 (GT37). Rocha
and coworkers solved the crystal structures of
the soluble portion of FUT1 both in the apo
form and bound to GDP and a xyloglucan
oligosaccharide acceptor. The most similar
known
structures
were
those
of
fucosyltransferases from other GT families,
including Caenorhabditis elegans POFUT1
and human POFUT2, which mediate Ofucosylation of proteins in those species.
These related structures have a GT-B fold,
which canonically includes two α/β/α
Rossmann-fold domains, termed the N- and Cdomains, with the active site in a cleft between
them. The FUT1 structure represents a GT-B
variant not previously observed (see figure).
Instead of the α/β/α N-domain, the FUT1 Ndomain has a β-sheet with α-helices on one
side, but loops on the other. The C-domain has
a more typical Rossmann fold, but an extra Cterminal domain forms β-hairpins that lie
against the N-domain. This extra domain
contacts both the N- and C-domains, and
forms part of the acceptor binding site.
The mechanism of GDP binding by FUT1
appears to be quite similar to that in the four
FUT1 adopts a variant of the GT-B superfamily fold. A, FUT1 structure reported in this
work. B and C, two of the most similar reported structures, (B) POFUT1 (PDB code 3ZY6) and
(C) POFUT2 (PDB code 4AP5). D, canonical GT-B fold of the phage T4-glucosyltransferase
(BGT, PDB code 1BGT), with two similar Rossmann domains: the N-domain (blue) and the Cdomain (green). (Adapted from Rocha et al., 2016, Supplemental Figure 1.)
most similar structures, despite FUT1 sharing
less than 20% sequence identity with the
corresponding proteins. Importantly, the
conserved residues involved in binding include
those in three motifs (I, II, III) that were
previously reported to be important for GT
activity. Thus, the FUT1 structure
demonstrates that these residues are
necessary for GT activity because of their
importance in donor sugar binding.
The authors also use the structure to
explain FUT1’s substrate specificity. In
contrast to the second galactosyl in the
acceptor subunit, the first residue is on the
opposite side of the β-1,4-D-glucan backbone
and does not make any contact with FUT1.
Accordingly, FUT1 fucosylates the second, but
not the first, galactosyl residue in a xyloglucan
acceptor. The extra C-terminal domain of
FUT1 also interacts with acceptor. Interestingly,
this domain is present in all ten Arabidopsis
GT37 family members, among which only
FUT1 acts on xyloglucan. Rocha et al. were
able to divide this family into three sub-groups,
based on their sequences in the region that
contributes to the anchoring of the xyloglucan
subunit in FUT1. Their analysis provides an
opening into predictions of substrate specificity
based on primary sequence, which has proved
quite difficult among GT family members.
Overall, this work adds another first to the
rich history of fucosyltransferase research in
plants and provides insight into the
biosynthesis of an important plant cell wall
component as well as into the function of the
huge family of glycosyltransferases in general.
Nancy R. Hofmann
Science Editor
[email protected]
ORCID ID: 0000-0001-9504-1152
REFERENCES
Pauly, M., and Keegstra, K. (2016).
Biosynthesis of the plant cell wall matrix
polysaccharide xyloglucan. Annu. Rev. Plant
Biol. 67: 235-259.
Rocha, J., Cicéron, F., de Sanctis, D.,
Lelimousin, M., Chazalet, V., Lerouxel, O.,
and Breton, C. (2016). Structure of
Arabidopsis thaliana FUT1 Reveals a Variant
of the GT-B Class Fold and Provides Insight
into Xyloglucan Fucosylation. Plant Cell. doi:
10.1105/tpc.16.00519
©2016 American Society of Plant Biologists. All Rights Reserved
Parsed Citations
Pauly, M., and Keegstra, K. (2016). Biosynthesis of the plant cell wall matrix polysaccharide xyloglucan. Annu. Rev. Plant Biol. 67:
235-259.
Pubmed: Author and Title
CrossRef: Author and Title
Google Scholar: Author Only Title Only Author and Title
Rocha, J., Cicéron, F., de Sanctis, D., Lelimousin, M., Chazalet, V., Lerouxel, O., and Breton, C. (2016). Structure of Arabidopsis
thaliana FUT1 Reveals a Variant of the GT-B Class Fold and Provides Insight into Xyloglucan Fucosylation. Plant Cell. doi:
10.1105/tpc.16.00519.
Pubmed: Author and Title
CrossRef: Author and Title
Google Scholar: Author Only Title Only Author and Title
Another Step Closer to Understanding Plant Cell Wall Biosynthesis: The Crystal Structure of
FUCOSYLTRANSFERASE 1
Nancy Rosenbaum Hofmann
Plant Cell; originally published online September 28, 2016;
DOI 10.1105/tpc.16.00756
This information is current as of August 10, 2017
Supplemental Data
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