Does Noggin head a new class of Kunitz domain?

the C2 consensus.The lack of complete similarity might be expected on functional grounds, since Ca 2"independent PKCs do not bind phosphatidylserine in a Ca2"-dependent fashion 7"9.PKCs 6, ¢ and ~ show little similarity in this region (Fig. Ib), suggesting that these isoforms may not be regulated in the same way as PKCs containing the E region.In Aplysia neurons, we find that the activation of Apl II, a Ca~Hndependent PKC isoform, requires factors in addition to diacylgiycerol 9.It is attractive to think that these as yet unidentified factors act by increasing the affinity of the E2 domain for phosphatidylserine in a manner analogous to the way Ca 2" affects the binding of phosphatidylserine to C2.This idea provides a working hypothesis for understanding the mechanism by which the E region may regulate the activation of these isoforms of PKC.