An Off-Pathway Folding Intermediate of an Acyl Carrier Protein Domain Coexists with the Folded and Unfolded States under Native Conditions

A protein can exist in multiple states under native conditions and those states with low populations are often critical to biological function and self‐assembly. To investigate the role of the minor states of an acyl carrier protein, NMR techniques were applied to determine the number of minor states and characterize their structures and kinetics. The acyl carrier protein from Micromonospora echinospora was found to exist in one major folded state (95.2 %), one unfolded state (4.1 %), and one intermediate state (0.7 %) under native conditions. The three states are in dynamic equilibrium and the intermediate state very likely adopts a native‐like structure and is an off‐pathway folding product. The intermediate state may mediate the formation of oligomers in vitro and play an important role in the recognition of partner enzymes in vivo. Abseits des Pfades: Acyl‐Trägerprotein aus Micromonospora echinospora nimmt drei Konformationen ein – eine gefaltete (N), eine nichtgefaltete (U) und eine intermediäre (I) –, die unter nativen Bedingungen langsam ineinander übergehen. Der intermediäre Zustand, der nicht auf dem Faltungspfad zu liegen scheint, könnte in vitro die Oligomerbildung vermitteln und in vivo eine wichtige Rolle bei der Erkennung von Partnerenzymen spielen.