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SUMO (small ubiquitin-related modifier) is a member of the ubiquitin-like
protein family that regulates cellular function of a variety of target proteins.
SUMO proteins are expressed as their precursor forms. Cleavage of the residues
after the 'GG' region of these precursors by SUMO-specific proteases in
maturation is a prerequisite for subsequent sumoylation. To understand further
this proteolytic processing, we expressed and purified SENP1 (sentrin-specific
protease 1), one of the SUMO-specific proteases, using an Escherichia coli
expression system. We show that SENP1 is capable of processing all SUMO-1, -2
and -3 in vitro; however, the proteolytic efficiency of SUMO-1 is the highest
followed by SUMO-2 and -3. We demonstrate further that the catalytic domain of
SENP1 (SENP1C) alone can determine the substrate specificity towards SUMO-1, -2
and -3. Replacement of the C-terminal fragments after the 'GG' region of SUMO-1
and -2 precursors with that of the SUMO-3, indicates that the C-terminal
fragment is essential for efficient maturation. In mutagenesis analysis, we
further map two residues immediately after the 'GG' region, which determine the
differential maturation. Distinct patterns of tissue distribution of SENP1,
SUMO-1, -2 and -3 are characterized. Taken together, we suggest that the
observed differential maturation process has its physiological significance in
the regulation of the sumoylation pathway.
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