# Accurate measurements of phasing signal to determine macromolecular structures

> **NIH NIH R01** · UT SOUTHWESTERN MEDICAL CENTER · 2020 · $317,580

## Abstract

Project summary
The proposal “Accurate measurements of phasing signal to determine macromolecular structures” aims to
broaden the applicability of experimental phasing methods, which are an essential component of solving novel
structures by X-ray crystallography. The proposed work is significant to the mission of the NIH is due to the
importance of X-ray crystallography, which generates uniquely detailed information about cellular processes at
the atomic level. This information is used to explain and validate results that are obtain by other biochemical
and biophysical techniques, to generate hypotheses for detailed studies of cellular processes by means of
orthogonal techniques, and to directly guide drug design studies.
Macromolecular crystals are frequently of limited size and crystal lattice order, which leads to decreased
quality of phasing signals. Thus, experimentalists average phasing signals across multiple data sets to obtain
accurate estimates and to decrease the impact of random errors. The averaging may be performed on data
sets acquired from the same crystal but at different wavelengths, different crystals that have been uniformly
derivatized with a heavy atom, or data sets collected from different crystals that have not been derivatized
uniformly, e.g. different concentrations of heavy atoms were applied during soaking. The averaging of data
sets is a challenge because of non-isomorphism between crystals, which may have different impacts on native
vs. phasing signals. Additionally, although averaging decreases random errors, the systematic effects in X-ray
experiments are not amenable to averaging in the same manner. The optimal approach to diffraction data
analysis in the presence of systematic effects is to identify the sources of these effects, and to either eliminate
their impact by redesigning the experiment or to filter out their contribution to the phasing signal by applying
software corrections.
There are several groups of presently uncorrected systematic effects that we have identified and which result
in significant distortion of estimates for phasing signals. We propose to develop novel and innovative software
corrections to address these problems. In Aim 1, we will develop and implement corrections for systematic
inefficiencies present in the signals produced by the current detectors and resulting from sample vibration and
complex absorption. In Aim 2, we will develop and implement a novel framework to optimally model the
phasing component of the signal obtained by averaging multiple, not-necessarily uniform data sets. In Aim 3,
we will develop approaches to filter out uninformative components of the measured intensity, so that the final
estimates of the phasing signal are optimal. In Aim 4, a secure, web-based server will be implemented so that
the structural community can use our methods, as a complement to the stand-alone software developed in
Aims 1-3.

## Key facts

- **NIH application ID:** 9861249
- **Project number:** 5R01GM118619-04
- **Recipient organization:** UT SOUTHWESTERN MEDICAL CENTER
- **Principal Investigator:** ZBYSZEK OTWINOWSKI
- **Activity code:** R01 (R01, R21, SBIR, etc.)
- **Funding institute:** NIH
- **Fiscal year:** 2020
- **Award amount:** $317,580
- **Award type:** 5
- **Project period:** 2017-05-01 → 2022-07-31

## Primary source

NIH RePORTER: https://reporter.nih.gov/project-details/9861249

## Citation

> US National Institutes of Health, RePORTER application 9861249, Accurate measurements of phasing signal to determine macromolecular structures (5R01GM118619-04). Retrieved via AI Analytics 2026-05-24 from https://api.ai-analytics.org/grant/nih/9861249. Licensed CC0.

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