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Figure 8.
FIGURE 8. Schematic diagram of the proposed autoactivation
mechanism of MASP-2. The CCP1-CCP2 moiety is shown as dotted
ellipses, and the SP domain is shown as a gray blob with the
activation peptide represented as a black loop. The flexible
CCP2/SP junction helps in orienting the SP domains (gray arrows)
in the physiological MBL ·MASP-2 complex. A, during "step
1" the zymogen molecule (left) cleaves another zymogen molecule
(right). In their initial complex, in addition to favorable
contacts (white arrows), unfavorable interactions (black arrows)
are also present, and the inactive/active-like conformational
transition of the enzyme SP domain (from light gray to gray
striped) is promoted. After the enzyme reaction, the product
(dark gray SP) is released. B, during "step 2," the activated
(left, dark gray SP) and zymogen (right, light gray SP) MASP-2
play the roles of the enzyme and the substrate, respectively. In
contrast to step 1, here the binding surface of the enzyme and
the substrate is preformed to make the canonical Michaelis
complex prior to the enzyme reaction.
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