Effect on resolution

Hope, H.

doi:10.1107/97809553602060000672

International
Tables for
Crystallography
Volume F
Crystallography of biological macromolecules
Edited by M. G. Rossmann and E. Arnold

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International Tables for Crystallography (2006). Vol. F. ch. 10.1, p. 197 | 1 | 2 |

Section 10.1.1.3. Effect on resolution

H. Hope^a ^*

^aDepartment of Chemistry, University of California, Davis, One Shields Ave, Davis, CA 95616-5295, USA
Correspondence e-mail: hhope@ucdavis.edu

10.1.1.3. Effect on resolution

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The effects on radiation damage and mechanical stability are clear-cut, and provide the main reasons for using cryotechniques. Resolution can also be affected, but the connection between temperature and resolution is neither simple nor obvious. If low resolution is the result of rapid radiation damage, lowering the temperature can lead to much improved resolution. However, if low resolution is mainly caused by inexact replication from one unit cell to another, lowering the temperature may have little effect on resolution. If the mosaic spread in the crystal increases upon cooling, resolution may even deteriorate.

In a model proposed by Hope (1988), a relationship between resolution r and temperature T is given by $[r_{2} = r_{1}[(B_{0} + bT_{2})/(B_{0} + bT_{1})]^{1/2}.]$ Here $[r_{1}]$ is the resolution at $[T_{1}]$ , $[r_{2}]$ is the resolution at $[T_{2}]$ , $[B_{0}]$ is the value of B at [T = 0] and b is a proportionality constant. The underlying assumption is that for any given temperature, the temperature factor [i.e. $[\exp(-B\sin^{2}\theta/\lambda^{2})]$ ] at the resolution limit has the same value; thus the effects of scattering factors and Lp factors are ignored. We see that if $[B_{0}]$ is the predominant term, lowering T will not have much effect, whereas for small $[B_{0}]$ (a relatively well ordered structure) the effect of T on r can be large. For example, if the room-temperature resolution is 1.5 Å, the resolution at 100 K can be around 1 Å, but if the room-temperature resolution is around 3 or 4 Å, little change can be expected. A qualitative assessment of these effects was clearly stated by Petsko (1975).

References

Hope, H.(1988). Cryocrystallography of biological macromolecules: a generally applicable method. Acta Cryst. B44, 22–26.Google Scholar

Petsko, G. A. (1975). Protein crystallography at sub-zero temperatures: cryoprotective mother liquors for protein crystals. J. Mol. Biol. 96, 381–392.Google Scholar

International Tables for Crystallography (2006). Vol. F. ch. 10.1, p. 197