4M4L: The structure of Cu T6 bovine insulin

Using synchrotron radiation (SR), the crystal structures of T6 bovine insulin complexed with Ni(2+) and Cu(2+) were solved to 1.50 and 1.45 A resolution, respectively. The level of detail around the metal centres in these structures was highly limited, and the coordination of water in Cu site II of the copper insulin derivative was deteriorated as a consequence of radiation damage. To provide more detail, X-ray absorption spectroscopy (XAS) was used to improve the information level about metal coordination in each derivative. The nickel derivative contains hexacoordinated Ni(2+) with trigonal symmetry, whereas the copper derivative contains tetragonally distorted hexacoordinated Cu(2+) as a result of the Jahn-Teller effect, with a significantly longer coordination distance for one of the three water molecules in the coordination sphere. That the copper centre is of type II was further confirmed by electron paramagnetic resonance (EPR). The coordination distances were refined from EXAFS with standard deviations within 0.01 A. The insulin derivative containing Cu(2+) is sensitive towards photoreduction when exposed to SR. During the reduction of Cu(2+) to Cu(+), the coordination geometry of copper changes towards lower coordination numbers. Primary damage, i.e. photoreduction, was followed directly by XANES as a function of radiation dose, while secondary damage in the form of structural changes around the Cu atoms after exposure to different radiation doses was studied by crystallography using a laboratory diffractometer. Protection against photoreduction and subsequent radiation damage was carried out by solid embedment of Cu insulin in a saccharose matrix. At 100 K the photoreduction was suppressed by approximately 15%, and it was suppressed by a further approximately 30% on cooling the samples to 20 K.
PDB ID: 4M4LDownload
MMDB ID: 116665
PDB Deposition Date: 2013/8/7
Updated in MMDB: 2018/06
Experimental Method:
x-ray diffraction
Resolution: 1.45  Å
Source Organism:
Similar Structures:
Biological Unit for 4M4L: dimeric; determined by author and by software (PISA)
Molecular Components in 4M4L
Label Count Molecule
Proteins (2 molecules)
Insulin(Gene symbol: INS)
Molecule annotation
Insulin(Gene symbol: INS)
Molecule annotation
Chemical (1 molecule)
* Click molecule labels to explore molecular sequence information.

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