1.B.14.5.1
HasR receptor-HasA haemophore heme receptor complex (HasA, an extracellular heme binding protein, binds one heme and transfers it directly to HasR, which uses HasB (2.C.1.1.2) (a TonB homologue) instead of TonB (2.C.1.1.1) for energization) (Benevides-Matos et al., 2008; Izadi-Pruneyre et al., 2006; Lefèvre et al., 2008; Benevides-Matos and Biville, 2010). A signaling domain in HasR interacts with a partially unfolded periplasmic domain of an antisigma factor, HasS, to control transcription by an ECF sigma factor (Malki et al. 2014).  The HasR domain responsible for signal transfer is highly flexible in two stages of signaling, extends into the periplasm at about 70 to 90 A from the HasR beta-barrel and exhibits local conformational changes in response to the arrival of signaling activators (Wojtowicz et al. 2016).