Heme Binding Constricts the Conformational Dynamics of the Cytochrome b₅₅₉′ Heme Binding Cavity

Abstract

Cytochrome b(559)' is a transmembrane protein formed by homodimerization of the 44-residue PsbF polypeptide and noncovalent binding of a heme cofactor. The PsbF polypeptide can dimerize in the absence and presence of heme. To monitor structural alterations associated with binding of heme to the apo-cytochrome, we analyzed the apo- and holo-cytochrome structure by electron paramagnetic resonance spectroscopy. Spin labeling of amino acids located close to the heme binding domain of the cytochrome revealed that the structure of the heme binding domain is unconstrained in the absence of heme. Heme binding restricts the conformational dynamics of the heme binding domain, resulting in the structurally more constricted holo-cytochrome structure.

In vivo reconstitution of a homodimeric cytochrome b559 like structure: The role of the N-terminus α -subunit from Synechocystis sp. PCC 6803

“…First, the polypeptides enter the membrane matrix; second, an α-helix interacts with and recognizes another α-helix at the conserved glycine and phenylalanine residues near the thylakoid lumen surface to make a (α/β) heterodimer; and third, the heme group is incorporated to coordinate the two histidines and form a mature holoprotein. According to our data and other results (Volkmer et al 2006); Ackdogan et al 2012), the heme group seems not to be necessary for the incorporation, recognition and stable assembly of the protein complex subunits. The consecutively maturation steps would be as the following:…”

“…Furthermore, our data suggest that the photosynthetic natural Cyt b 559 assembly and maturation would most probably occur by a three step model as demonstrated for the (β/β) homodimer in (Volkmer et al 2006;Ackdogan et al 2012). First, the polypeptides enter the membrane matrix; second, an α-helix interacts with and recognizes another α-helix at the conserved glycine and phenylalanine residues near the thylakoid lumen surface to make a (α/β) heterodimer; and third, the heme group is incorporated to coordinate the two histidines and form a mature holoprotein.…”

Spontaneous Adhesion of DOPA and Tryptophan Functionalized PEG to Polystyrene Nanobeads: An EPR Study

“…Therefore, this technique is useful for studying metal complexes, inorganic and organic radicals, protein structures, drug delivery and surface defects, etc. [7][8][9][10][11][12][13]. Spin labeling of polystyrene (PS) in combination with EPR technique allows us to monitor the surface of nanobeads in solution [5,6].…”

The soluble loop BC region guides, but not dictates, the assembly of the transmembrane cytochrome b6

“…b 6 [ 8 , 28 – 32 ] or cyt. b 559 [ 9 , 33 – 37 ] have indicated that the respective holo-cytochromes spontaneously assemble in vitro and in vivo in presence of heme. The two b-type hemes of in vitro reconstituted cyt.…”