High-resolution structure of human cytoglobin: identification of extra N- and C-termini and a new dimerization mode

Cytoglobin ( Cgb) is a recently discovered member of the vertebrate haem-containing globin family. The structure of a new crystal form of wild-type human Cgb ( space group C2) was determined at a resolution of 1.68 (A) over circle. The results show the presence of an additional helix in the N-terminal residues ( 4-20) prior to the A helix and an ordered loop structure in the C-terminal region ( 168-188), while these extended peptides were invisible owing to disorder in the previously reported structures using a P3(2)21 crystal at a resolution of 2.4 (A) over circle. A detailed comparison of the two crystal structures shows differences in the conformation of the residues ( i.e. Arg84) in the haem environment owing to a different dimeric arrangement.