The mosquitocidal toxin (MTX) from @entity11304 SSII-1 is a approximately 97-kDa protein sharing sequence homology within the N terminus with the catalytic domains of various bacterial ADP-ribosyltransferases. Here we studied the proteolytic activation of the ADP-ribosyltransferase activity of MTX. Chymotrypsin treatment of the 97-kDa MTX holotoxin (MTX(30-870)) results in a 70-kDa putative binding component (MTX(265-870)) and a 27-kDa enzyme component (MTX(30-264)), possessing ADP-ribosyltransferase activity. Chymotryptic cleavage of an N-terminal 32-kDa fragment of MTX (MTX(30-308)) also yields MTX(30-264), but the resulting ADP-ribosyltransferase activity is much greater than that of the processed MTX(30-870). Kinetic studies revealed a K(m) NAD value of 45 microm for the processed 32-kDa MTX fragment, and a K(m) NAD value of 1300 microm for the processed holotoxin. Moreover, the k(cat) value for the activated MTX(30-308) fragment was about 10-fold higher than that for the activated holotoxin (MTX(30-870)). Precipitation analysis showed that the 70-kDa proteolytic fragment of MTX remains noncovalently bound to the N-terminal 27-kDa fragment, thereby inhibiting ADP-ribosyltransferase and NAD glycohydrolase activities. Glu(197) of MTX(30-264) was identified as the "catalytic" glutamate that is conserved in all ADP-ribosyltransferases. Whereas mutated MTX(30-264) @entity69618 has neither ADP-ribosyltransferase nor NAD glycohydrolase activity, mutated MTX(30-264) @entity69619 possesses glycohydrolase activity but not transferase activity. Transfection of HeLa cells with a vector encoding a fusion protein of MTX(30-264) with a green fluorescent protein led to cytotoxic effects characterized by cell rounding and formation of filopodia-like protrusions. These cytotoxic effects were not observed with the catalytically inactive MTX(30-264) @entity69618 mutant, indicating that the MTX enzyme activity is essential for the @entity137 in @entity1 cells.

The ADP-ribosylating mosquitocidal toxin from XXXX : proteolytic activation, enzyme activity, and cytotoxic effects.

@entity1 :: ('9606', 'Species') :: ['mammalian'] @entity137 :: ('MESH:D064420', 'Disease') :: ['cytotoxicity'] @entity69619 :: ('p|SUB|E|195|Q', 'ProteinMutation') :: ['E195Q'] @entity69618 :: ('p|SUB|E|197|Q', 'ProteinMutation') :: ['E197Q'] @entity11304 :: ('1421', 'Species') :: ['Bacillus sphaericus']
@entity11304 :: (1421,Species) :: ['Bacillus sphaericus']
