Intensity to amplitude conversion usingCTRUNCATE
Norman Stein, Charles Ballard · Acta Crystallographica Section A Foundations of Crystallography · 2009
Comprehensive structural interpretation of the crystallographic experimental X-ray data, having both observed structure factor amplitudes and phase estimates, remains one of the most challenging tasks in the protein crystallography.Our on-going development is addressed to the problem of performing accuracy and completeness of the protein structure provided by the protein chain tracing module of ARP/wARP software.The success of the model building strongly depends on the level of the informational content of the data, where a low level is indicated by noisy structure factors leading to a hardly interpretable electron density map or by the data, whose resolution is limited.We combine several methods including weighted template matching technique and optimisation of the density template alignment.We apply a number of rotation invariant characteristics defined on the density values and centre-atomic distances.This leads to the completeness of the model that is growing from iteration to iteration.We also introduce a resolution dependent parameter, which further increase the completeness of the provided structure.Overall the improvement of the built main chain by 12-25% is achieved compared to the protein chain tracing in earlier ARP/wARP version 7.0.