Conformationally constrained analogues of diacylglycerol (DAG).: 15.: The indispensable role of the sn-1 and sn-2 carbonyls in the binding of DAG-lactones to protein kinase C (PK-C)

The binding mode of DAG-lactones to PK-C was investigated using the C1b domain from the Xray structure of the phorbol ester/C1b complex of PK-C delta as a template. Modeling experiments revealed two binding alternatives in which one of the carbonyls of the DAG lactones remained uninvolved with the protein. Experimentally, however, the removal of either sn-1 or sn-2 carbonyls caused a dramatic drop in binding affinity towards PK-C. Although it was not possible to discriminate between the two binding alternatives of the DAG-lactones, the study demonstrates an important role for the additional carbonyl group. The function of this group could be equivalent to that of the C-9(OH)/C-13 (C=O) motif in phorbol esters, which also appears free of interactions in the phorbol ester/C1b complex. This role presumably reflects interaction with the phosholipid head groups required for high affinity binding under the conditions of the biological assays. (C) 1998 Elsevier Science Ltd. All rights reserved.