Structural heterogeneity of pseudomonas aeruginosa bacterioferritin

The subunit composition, amino acid sequence and haem-binding characteristics of bacterioferritin (BFR) from Pseudomonas aeruginosa have been studied. Unlike other BFRs, P. aeruginosa BFR was found to contain two subunit types, designated α and β, which differed considerably in their amino acid sequences. The N-terminal 69 and 55 amino acids of the α and β subunits respectively were determnined. The α subunit differed most from other BFRs. The two subunits were present in variable proportions in different preparations. The maximum stoichiometry of haem binding was found to be sample-dependent and to be different from the previously reported one per subunit. This previous haem-binding study was shown to have been carried out with damaged protein, which contained both normal α and β subunits and shorter versions of these that appeared to have been produced by cleavage of the normal subunits. The possibility that aging processes degrade ferritins and affect their haem-binding characteristics is discussed.