Structure-function analysis of the heme-binding WWD domain in the bacterial holocytochrome synthase, CcmFH.

Heme is an essential co-factor for proteins involved with critical cellular functions, such as energy production and oxygen transport. Thus, understanding how heme interacts with proteins and is moved through cells is a fundamental biological question. This work studies the System I cytochrome biogenesis pathway, which in some species (including ) is composed of eight integral membrane or membrane-associated proteins called CcmA-H that are proposed to function in two steps to transport and attach heme to apocytochrome . Cytochrome requires this heme attachment to function in electron transport chains to generate cellular energy. A conserved WWD heme-handling domain in CcmFH is analyzed and residues critical for heme interaction and holocytochrome synthase activity are identified. CcmFH is the third member of the WWD domain-containing heme-handling protein family to undergo a comprehensive structure-function analysis, allowing for comparison of heme interaction across this protein family.