CRYSTAL STRUCTURE OF THE HUMAN ADENOVIRUS PROTEASE WITH ITS 11 AMINO-ACID COFACTOR AT 1.6Å RESOLUTION. Jianzhong Ding, William J. McGrath, Walter F. Mangel, and Robert M. Sweet, Biology Department, Brookhaven National Laboratory, Upton, New York 11973
The human adenovirus serotype 2 protease (AVP) is essential for the production of infectious virus. Its function is to cleave multiple copies of 6 different virion proteins 2500 times to render a virus particle infectious. It is unique in that it requires two cofactors for maximal activity. One cofactor is pVIc, the 11 amino-acid peptide from the C-terminus of adenovirus precursor protein pVI. The second cofactor is viral DNA. The cofactors stimulate the catalytic rate constant 350-fold with pVIc, and 6000-fold with pVIc plus the viral DNA. Comparison of the structure of AVP with the cysteine protease papain and the chymotrypsin-like cysteine proteases indicates that AVP has a new fold. Thus, AVP represents a new subclass of cysteine protease.
We have extended the resolution of our previously reported X-ray structure of AVP with its pVIc cofactor from 2.6Å to 1.6Å through the use of a flash-frozen crystal. We used both programs X-PLOR and SHELXL to produce a final model at 1.6-Å resolution with Rworking = 13.3%, and Rfree = 17%.
In a related study, we solved the structures of this complex where the cofactor peptide pVIc was replaced by two mutant peptides in which the cysteine residue was replaced by either serine or alanine. Both mutant peptides are capable of serving as cofactors, although with altered affinities for the protease. The high-resolution structure has become the basis for structure-based rational drug design, and the structures with the mutants of pVIc have provided insights into the structural basis of cofactor activity.
This work was supported by National Institute of Allergy and Infectious Diseases Grant AI26049, by the Office of Health and Environmen tal Research of the United States Department of Energy and by the National Science Foundation.