Improving the convergence rate of a hybrid input–output phasing algorithm by varying the reflection data weight

2018 ◽  
Vol 74 (1) ◽  
pp. 36-43 ◽  
Author(s):  
Hongxing He ◽  
Wu-Pei Su

In an iterative projection algorithm proposed forab initiophasing, the error metrics typically exhibit little improvement until a sharp decrease takes place as the iteration converges to the correct high-resolution structure. Related to that is the small convergence probability for certain structures. As a remedy, a variable weighting scheme on the diffraction data is proposed. It focuses on phasing low- and medium-resolution data first. The weighting shifts to incorporate more high-resolution reflections when the iteration proceeds. It is found that the precipitous drop in error metrics is replaced by a less dramatic drop at an earlier stage of the iteration. It seems that once a good configuration is formed at medium resolution, convergence towards the correct high-resolution structure is almost guaranteed. The original problem of phasing all diffraction data at once is reduced to a much more manageable one due to the dramatically smaller number of reflections involved. As a result, the success rate is significantly enhanced and the speed of convergence is raised. This is illustrated by applying the new algorithm to several structures, some of which are very difficult to solve without data weighting.

1999 ◽  
Vol 55 (4) ◽  
pp. 801-809 ◽  
Author(s):  
Stephen W. White ◽  
Keith S. Wilson ◽  
Krzysztof Appelt ◽  
Isao Tanaka

Protein HU is a ubiquitous prokaryotic protein which controls the architecture of genomic DNA. It binds DNA non-specifically and promotes the bending and supercoiling of the double helical structure. HU is involved in many DNA-associated cellular processes, including replication, transcription and the packaging of DNA into chromosome-like structures. Originally determined at medium resolution, the crystal structure of HU has now been refined at 2.0 Å resolution. The high-resolution structure shows that the dimeric molecule is essentially a compact platform for two flexible and basic arms which wrap around the DNA molecule. To maximize the protein's stability, non-secondary structural regions are reduced to a minimum, there is an extensive aromatic hydrophobic core and several salt bridges and hydrogen-bonded water molecules knit together crucial regions. Based on the original medium-resolution structure of HU, several proposals were made concerning the structural basis of HU's ability to bind, bend and supercoil DNA. Each of these proposals is fully supported by the high-resolution structure. Most notably, the surfaces of the molecule which appear to mediate protein–DNA and protein–protein interactions have the ideal shapes and physicochemical properties to perform these functions.


2014 ◽  
Vol 11 (9) ◽  
pp. 927-930 ◽  
Author(s):  
Brent L Nannenga ◽  
Dan Shi ◽  
Andrew G W Leslie ◽  
Tamir Gonen

FEBS Letters ◽  
2010 ◽  
Vol 584 (12) ◽  
pp. 2539-2547 ◽  
Author(s):  
Yo Sonoda ◽  
Alex Cameron ◽  
Simon Newstead ◽  
Hiroshi Omote ◽  
Yoshinori Moriyama ◽  
...  

Cell ◽  
2001 ◽  
Vol 107 (5) ◽  
pp. 679-688 ◽  
Author(s):  
Joerg Harms ◽  
Frank Schluenzen ◽  
Raz Zarivach ◽  
Anat Bashan ◽  
Sharon Gat ◽  
...  

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