Alternate locations of backbones

At sufficiently high resolution, empirical methods for determining macromolecular structure may detect multiple locations for some atoms, termed alternate locations. When alternate locations for backbones deviate substantially, the backbone may separate into two pathways ("fork") and then rejoin into a single pathway.

Alternate location serverAlternate location server

An Alternate Location Server (AltLoc Server) (part of the OCA Browser system) scans all entries in the Protein Data Bank, listing those that have alternate locations. The analysis below is based on an AltLoc Server report from late May, 2023, when the total number of entries in the PDB was ~200,700. Here are two example lines from the report:

ID    Method            Res   Dep Date
9ins  X-ray diffraction 1.70  1991-10-23  min=-1.0  ave=-1.0  max=-1.0  A=48  B=48
4dgd  X-ray diffraction 1.4   2012-01-25  min=0.03  ave 4.78  max 15.87 A=84  B=84  A.CA=13  B.CA=13