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Molecular Function of NCAPP1
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Plasmodesmata play an important
role in regulating intercellular trafficking of non-cell-autonomous
proteins (NCAPs). We isolated a putative component of this NCAP
pathway, NtNCAPP1, from tobacco tissues using affinity chromatography
methods based on interaction with CmPP16, a demonstrated NCAP involved
in the intercellular trafficking of RNA (Lee et al., 2003, Figure
1). |
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Deletion of the ER-targeting trans-membrane domain
from NtNCAPP1 caused it to function as a gain-of-function dominant
negative mutant when expressed in tobacco. This mutant form could
block the trafficking of some, but not all, NCAPs, suggesting selectivity
of NCAPP1 function. NtNCAPP1 encodes a putative ER-targeted trans-membrane
protein with homology to aldose-1-epimerase (mutarotase) that is
involved in galactose metabolism in E.coli . However, whether
this enzymatic activity is required for NtNCAPP1 function remains
to be shown. |
To further investigate the molecular function of NCAPP1
in macromolecular trafficking through PD, we isolated NtNCAPP1 homologs
from Arabidopsis (Figure 2). |
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Four mutarotase isoforms (AtNCAPP1-A, -B, -C, and
-D) were identified in the Arabidopsis genome and AtNCAPP1-A
and AtNCAPP1-B contain the same putative ER-targeting trans-membrane
domain identified in NtNCAPP1. Although mutarotase genes are conserved
in a variety of organisms, from bacteria to mammals, our phylogenetic
analysis indicated that members of the mutarotase gene family having
this trans-membrane region were confined to the plant kingdom.
We are currently investigating the enzymatic activity of NCAPP1
and the phenotype of T-DNA insertion lines of AtNCAPP1 genes.
We will then isolate and characterize interaction partners of NCAPP1
in an effort to better define the underlying mechanism involved
in NCAP function in plants. |
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Reference
Lee, JY, Yoo, BC, Rojas, MR, Gomez-Ospina, N, Staehelin, LA and Lucas
WJ (2003) Selective trafficking of non-cell-autonomous proteins
mediated by NtNCAPP1. Science 299: 392-396 |
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