Eukaryotic Cell doi:10.1128/EC.00203-06
Copyright (c) 2006, American Society for Microbiology and/or the Listed Authors/Institutions. All Rights Reserved.
Prenylation of S. cerevisiae Chs4p affects chitin synthase III activity and chitin chain length
Kariona A. Grabi
ska*,
Paula Magnelli,
and
Phillips W. Robbins
Department of Molecular and Cell Biology, School of Dental Medicine, Boston University, 715 Albany Street, Evans 408 Boston, MA 02118
* To whom correspondence should be addressed. Email:
karionag{at}bu.edu,
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Abstract |
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Chs4p (Cal2/Csd4/Skt5) was identified as a protein factor physically interacting with Chs3p, the catalytic subunit of chitin synthase III (CSIII), and is indispensable for its enzymatic activity in vivo. Chs4p contains a putative farnesyl attachment site at the C-terminal end (CVIM-motif) conserved in Chs4p of S. cerevisiae and other fungi. Several previous reports questioned the role of Chs4p prenylation in chitin biosynthesis. In this study we reinvestigated the function of Chs4p prenylation. We provide evidence that Chs4p is farnesylated by showing that purified Chs4p is recognized by anti-farnesyl antibody, is a substrate for farnesyl transferase (FTase) in vitro, and that inactivation of FTase increases the amount of unmodified Chs4p in the yeast cells. We demonstrate that abolishing Chs4p prenylation causes 
60 % decrease in CSIII activity which is correlated with a 30 % decrease in the chitin content, and with increased resistance to the chitin binding compound, Calcofluor white. Furthermore, we show that lack of Chs4p prenylation decreases the average chain length of the chitin polymer. Prenylation of Chs4p, however, is not a factor which mediates plasma membrane association of the protein. Our results provide evidence that the prenyl moiety attached to the Chs4p is a factor modulating the activity of CSIII both in vivo and in vitro.
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