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pH dependence of the ADF/cofilins

 

Most members of the ADF/cofilin family are pH sensitive in their interaction with F-actin.  This was first reported by Yonezawa (Yonezawa et al, 1985).  In considering the pH dependency of protein protein interaction one invariably focuses on histidines as they uniquely have pKa values within the physiological range.  However, when we consider the pH dependency of the interaction between ADF/cofilins and F-actin it is obvious that the histidines that may be suspected of being at this interface are not conserved between the various species.

Actophorin is not pH sensitive as typical members of the group are.  Actophorin behaves with respect to F-actin as these other members do at pH 6.5 at all pH values tested (pH6.5 - 8.0) in other words actophorin binds F-actin or actin aggregates at pH 8.0 whereas other members of the group bind G-actin exclusively at this pH value.  The molecular mechanism for these differences are not presently known.  The plant ADF/cofilin ZmADF3 has been shown to be pH sensitive but the threshold pH value is shifted 

 

 
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