Highly malleable haem-binding site of the haemoprotein HasA permits stable accommodation of bulky tetraphenylporphycenes.

Iron(iii)- and cobalt(iii)-9,10,19,20-tetraphenylporphycenes, which possess bulky phenyl groups at the four meso positions of porphycene, were successfully incorporated into the haem acquisition protein HasA secreted by Pseudomonas aeruginosa . Crystal structure analysis revealed that loops surrounding the haem-binding site are highly flexible, remodelling themselves to accommodate bulky metal complexes with significantly different structures from the native haem cofactor.