I have recently solved a 2.0 angstrom resolution
structure. The structure is near complete but I have some
unusual density at the crystallographic interface between
two chains of different asymmetric units. The linked
photos show the density at with a Fo-Fc at 3 sigma and
2Fo-Fc at 1 sigma.
The center of the density is approximately 2.1 angtroms
from both the Asp sidechain and the carbonyl oxygen on the
other chain. I have attempted to fit in either calcium or
sodium atom and waters, but these attempts don't satisfy
the positive density while maintaining proper
coordination.
My buffer components are PIPES, NaCl, TCEP and the
crystallization conditions are PEG 1K, Calcium acetate,
Imidazole pH 8.0, and glycerol. Any insight as to what
this density could be would be greatly appreciated.
Thanks,
Jared Pitts
Jared Pitts
Doctoral
Student
Department
of Molecular Biology and Microbiology
Tufts
University School of Medicine
136
Harrison Avenue
Arnold Building Room 611
Boston,
MA 02139
