Mechanisms of Metal Resistance and Homeostasis in Haloarchaea

Table 4

ABC transporters with various functions present in some model haloarchaea. ABC transporters have three components that together help in uptake of nutrients or for the efflux of extracellular proteins, enzymes, and toxicants. Permease is the transmembrane component and is responsible for the uptake of ions or macromolecules, while the ATP-binding component is the water soluble domain that binds ATP. Substrate binding at the substrate binding site brings about a conformational change in the ATP-binding component resulting in ATP hydrolysis. The presence or absence of the three components of ABC transporters for sugar, peptide, amino acids, phosphate, and iron transport is shown in the following table [135, 136].

ABC transporters	H.s.	H.v.	H.m.	H.w.	H.l.	N.p.	N.m.
Sugar transport system components
Permease	+	+	+	+	−	−	−
ATP binding	+	+	+	+	−	−	−
Substrate binding	−	−	+	+	+	−	−
Phosphate transport system components
Permease	+	+	+	+	+	+	+
ATP binding	−	+	+	+	+	+	+
Susbtrate binding	+	+	+	+	+	+	+
Dipeptide/oligopeptide transport system components
Permease	+	+	+	+	−	+	−
ATP binding	+	+	+	+	+	+	+
Susbtrate binding	−	−	+	+	−	+	+
Amino acid transport system components
Permease	−	+	+	+	−	+	−
ATP binding	+	+	+	+	−	+	−
Susbtrate binding	−	+	−	+	+	+	+
Fe(III) transport system components
Permease	+	+	+	+	−	+	+
ATP binding	+	+	−	−	−	+	−
Susbtrate binding	−	−	−	+	+	+	−

H.s., Halobacterium sp. strain NRC-1; H.v., Haloferax volcanii; H.m., Haloarcula marismortui; H.w. Haloquadratum walsbyi; H.l., Halorubrum lacusprofundi; N.p, Natronomonas pharaonis; Natrialba magadii; (+) present; (−) absent.