Bioinformatics Vol. 17 no. 10 2001
Pages 965-976
© 2001 Oxford University Press
Sequence and structural aspects of functional diversification in class I 
-mannosidase evolution
1 National Center for Biotechnology
Information, National Library of Medicine, National Institutes of
Health, Bethesda, MD 20894, USA
2 Department of Chemistry, Millsaps College,
Jackson, MS 39210, USA
3 United States Department of Agriculture,
Aquatic Animal Health Research Unit, Auburn, AL 36831, USA
Received on April 20, 2001
; revised on July 12, 2001
; accepted on July 12, 2001
Motivation: Class I 
-mannosidases comprise a
homologous and functionally diverse family of glycoside hydrolases.
Phylogenetic analysis based on an amino acid sequence alignment of
the catalytic domain of class I -mannosidases reveals
four well-supported phylogenetic groups within this family. These
groups include a number of paralogous members generated by gene
duplications that occurred as far back as the initial divergence of
the crown-group of eukaryotes. Three of the four phylogenetic groups
consist of enzymes that have group-specific biochemical specificity
and/or sites of activity. An attempt has been made to uncover the
role that natural selection played in the sequence and structural
divergence between the phylogenetically and functionally distinct
Endoplasmic Reticulum (ER) and Golgi apparatus groups.
Results: Comparison of site-specific amino acid variability
profiles for the ER and Golgi groups revealed statistically
significant evidence for functional diversification at the sequence
level and indicated a number of residues that are most likely to
have played a role in the functional divergence between the two
groups. The majority of these sites appear to contain residues that
have been fixed within one organelle-specific group by positive
selection. Somewhat surprisingly these selected residues map to the
periphery of the -mannosidase catalytic domain tertiary
structure. Changes in these peripherally located residues would not
seem to have a gross effect on protein function. Thus diversifying
selection between the two groups may have acted in a gradual manner
consistent with the Darwinian model of natural selection.
Contact: bishogr{at}millsaps.edu
* To whom correspondence should be addressed.
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