W0138

Density Modification to Aid Automatic Chain Tracing. Hao Wang¹, Albert Fu², Robert Harrison¹, ¹Dept. of Computer Science, Georgia State Univ., ²Dept. of Biochemistry and Molecular Biology, Univ. of Georgia, Atlanta, GA.

Density modification approaches greatly extend the utility of automated chain tracing for low and moderate resolution problems. Automated chain tracing using programs like ARP/wARP and solve/resolve is a useful and powerful technique when the resolution of the data and quality of the map are high enough. The programs are critically dependent on the map quality and do not work on maps at moderate resolutions. Unfortunately many proteins only diffract to moderate resolution and the phase quality of the high resolution phases tends to be low thus limiting the applicability of automated techniques. One potential solution to this dilemma is to use density modification techniques to improve the map quality. In order to understand the general applicability of density modification two techniques were tested. These were the ISAS solvent flattening suite, and a new program that used smooth kernels and the ant hill algorithm to solve the inequality that density is greater than zero were tested. Data from cubic Insulin were used and the phases were extended from 4,3.5, and 3Å to 2.1Å resolution. The maps were then traced by ARP/wARP. Successful traces were obtained by both programs in all cases, although the tracing from the ISAS suite at 4Å was more complete. On the other hand the new program produced maps where ARP/wARP converged more quickly.