Acyl carrier protein

The acyl carrier protein (ACP) is an important component in both fatty acid and polyketide biosynthesis with the growing chain bound during synthesis as a thiol ester at the distal thiol of a 4'-phosphopantetheine moiety. The protein is expressed in the inactive apo form and the 4'-phosphopantetheine moiety must be post-translationally attached to a conserved serine residue on the ACP by the action of holo-acyl carrier protein synthase (ACPS), a phosphopantetheinyl transferase.

4'-Phosphopantetheine is an essential prosthetic group of several acyl carrier proteins involved in pathways of primary and secondary metabolism including the acyl carrier proteins (ACP) of fatty acid synthases, ACPs of polyketide synthases, and peptidyl carrier proteins (PCP) and aryl carrier proteins (ArCP) of nonribosomal peptide synthetases (NRPS). Phosphopantetheine fulfills two demands in these biosynthetic pathways. First, the intermediates remain covalently linked to the synthases (or synthetases) in an energy-rich linkage. Second, the flexibility and length of the phosphopantetheine chain (approximately 2 nm) allows the covalently tethered intermediates to have access to spatially distinct enzyme-active sites. This increases the effective molarity of the intermediate and allows an assembly line-like process.

Carrier protein

Carrier proteins, (together with channel proteins) are Membrane transport proteins actively facilitating transport of molecules across cell membrane on which they are placed. Carrier proteins facilitate the diffusion of different molecules, to which they have specificity, one molecule at the time is allowed to bind to carrier protein and is released on the other side of the membrane. Carrier proteins are integral/intrinsic membrane proteins; that is they exist within and span the membrane across which they transport substances. The proteins may assist in the movement of substances by facilitated diffusion or active transport. These mechanisms of movement are known as carrier-mediated transport. Each carrier protein is designed to recognize only one substance or one group of very similar substances. Research has correlated defects in specific carrier proteins with specific diseases.

Active transportation

Active transport