Streptomyces lividans, potassium channel

Just as there are cation channels, there are also trans-membrane channels involved in the transport of biologically important anions such as Cl-. The crystal structure of the CIC chloride channel from Salmonella typhimurium was reported in 2002.3 Along with the determination of the Streptomyces lividans potassium channel structure, this work won a share of the 2003 Nobel prize in chemistry for Roderick MacKinnon (Howard Hughes Medical Institute, New York, USA). Chloride channels catalyse the flow of chloride across cell membranes and play a significant role in functions such as... 

PolyPs and PHB have been found to be associated with ion-conducting proteins such as the human erythrocyte Ca2+-ATPase pump (Reush et al, 1997) and the Streptomyces lividans potassium channel (Reusch, 1999b). Some enzymes of PolyP metabolism, such as polyphosphate glucokinase (Phillips et al, 1999) and yeast high-molecular-weight exopolyphosphatase (Andreeva et al, 2001, 2004), can contain tightly bound PolyP. 

One of the characteristics of protein calcium channels is their sensitivity to ablock by transition metal cations. Lanthanum is a particularly potent blocker. It is suggested that permeant and blocking ions compete for the common binding sites in the channels. The PolyP-PHB channel complexes are also blocked by transition metal cations in a concentration-dependent manner. A nearly complete block of single-channel currents was observed in the synthetic complexes at concentations > 0.1 mM La3+ (0.1 % of Ca2+) (Das et al., 1997). Evidently, PHB-PolyP complexes are versatile ion carriers whose selectivities may be modulated by small adjustments of the local pH. The results may be relevant to the physiological function of PHB-PolyP channels in bacteria and the role of PHBs and PolyPs in the Streptomyces lividans potassium channel (Das and Reusch, 2001). 

R. N. Reusch (1999b). Streptomyces lividans potassium channel contains poly-(R)-3-hydroxybutyrate and inorganic polyphosphate. Biochemistry, 38, 15666-15672. 

R575 B. A. Wallace, X-Ray Crystallographic Structures of Gramicidin and their Relation to the Streptomyces Lividans Potassium Channel Structure , Novartis Found Symp., 1999, 225, 23... 

Reusch RN (1999) Streptomyces lividans Potassium Channel Contains Poly-(R)-3-hydroxybutyrate and Inorganic Polyphosphate. 15666-15672. 

Zakharian E, Reusch RN (2004) Functional evidence for a supramolecular structure for the Streptomyces lividans potassium channel KcsA. Biochemical and Biophysical Research Communications 322 1059—1065. 

The Shaker potassium channel did not yield crystals for the first potassium ion channel X-ray crystallographic structure. Rather, it was the prokaryote bacterium Streptomyces lividans, abbreviated as the KcsA K+ channel, that first produced crystals suitable for crystallography. This structure, published in 1998 by MacKinnon s group in Science magazine, was received with great praise from the scientific community. It was known at that time that the amino acid sequence of KcsA was similar to that of other K channels, including vertebrate and invertebrate voltage-dependent K (Kv) channels (such as the... 

KcsA is a potassium channel protein from Streptomyces lividans that assembles as a tetramer.68 An X-ray diffraction study of a crystal defined the transmembrane and some extracellular portions of the structure but no structural information could be obtained for cytoplasmic domains. Since the protein assembles as a tetramer, when one spin label is present on each subunit, it is difficult to interpret the dipolar interactions because of the presence of adjacent... 

The presence of PHB and polyP in a human calcium pump indicates that the role of these polymers in ion transport has been conserved, and further suggests that the polymers are likely constituents of other ion channels and pumps. Recently, the potassium channel of the Gram-positive soil bacterium, Streptomyces lividans (KcsA), attracted great interest as the first ion channel to have its structure analyzed... 

Gross, A., Columbus, L., Hideg, K., Altenbach, C., and Hubbell, W. L. (1999). Structure of the KcsA potassium channel from Streptomyces lividans a site-directed spin labeling study of the second transmembrane segment. Biochemistry 38, 10324-10335. 

Meuser, D., Splitt, H., Wagner, R., and Schrempf, H. (1999). Exploring the open pore of the potassium channel from Streptomyces lividans. FEBS Lett. 462, 447-452. 

Schrempf, H., Schmidt, O., Kummerlen, R., Hinnah, S., Muller, D., Betzler, M., Steinkamp, T., and Wagner, R. (1995). A prokaryotic potassium ion channel with two predicted transmembrane segments from Streptomyces lividans. EMBOJ. 14, 5170-5178. 

An exciting model within these protein/polyP/PHB complexes has been represented by a potassium channel of Streptomyces lividans KcsA [44], [47]. Association of the polymers appears to contribute to the ion selectivity and gating properties of KcsA, and to determine its preference between mono- and divalent... 

Hegermann J, Lunsdorf H, Overbeck J, Schrempf HPolyphosphate at the Streptomyces lividans cytoplasmic membrane is enhanced in the presence of the potassium channel KcsAl74—182. 

The biocompatibility of PHAs originates from the fact that some monomers incorporated into the polymer chain occur naturally in the human body. The monomer (i )-3-hydroxybutyric acid is a normal metabohte found in human blood. This hydroxy acid is present at concentrations of 3 10 mg per 100 ml blood in healthy adults. Also low molecular weight PHAs are found com-plexed to other cellular macromolecules - hence they are called complexed PHAs (cPHAs). For example, cPHAs have been found in human tissues complexed with low-density lipoproteins, carrier protein albumin and in the potassium channel (KcsA) of Streptomyces lividans. Biocompatibility of PHAs, like any other biomaterial, is dependent on factors such as shape, surface porosity, surface hydrophilicity, surface energy, chemistry of the material and its degradation product. In tissue engineering, it is important that the... 

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