Biomedical subjects

J K Chugh

Publications and source records attributed to J K Chugh.

4 recordsLinked to original sources

PubMed2004

Conductance studies on trichotoxin_A50E and implications for channel structure.

Trichotoxin_A50E is an 18-residue peptaibol whose crystal structure has recently been determined. In this study, the conductance properties of trichotoxin_A50E have been investigated in neutral planar lipid bilayers. The macroscopic current-voltage curves disclose a moderate voltage-sensitivity and the concentration-dependence suggests the channels are primarily hexameric. Under ion gradients, shifts of the reversal potential indicate that cations are preferentially transported. Trichotoxin displays only one single-channel conductance state in a given experiment, but an ensemble of experiments reveals a distribution of conductance levels. This contrasts with the related peptaibol alamethicin, which produces multiple channel levels in a single experiment, indicative of recruitment of additional monomers into different multimeric-sized channels. Based on these conductance measurements and on the recently available crystal structure of trichotoxin_A50E, which is a shorter and straighter helix than alamethicin, a tightly-packed hexameric model structure has been constructed for the trichotoxin channel. It has molecular dimensions and surface electrostatic potential compatible with the observed conductance properties of the most probable and longer-lived channel.

Alamethicin↗

PubMed2002

Model for a helical bundle channel based on the high-resolution crystal structure of trichotoxin_A50E.

Trichotoxin_A50E is an 18-residue peptaibol antibiotic which forms multimeric transmembrane channels through self-association. The crystal structure of trichotoxin has been determined at a resolution of 0.9 A. The trichotoxin sequence contains nine helix-promoting Aib residues, which contribute to the formation of an entirely helical structure that has a central bend of 8-10 degrees located between residues 10-13. Trichotoxin is the first solved structure of the peptaibol family that is all alpha-helix as opposed to containing part or all 3(10)-helix. Gln residues in positions 6 and 17 produce a polar face, and are proposed to form the channel lumen. An octameric model channel has been constructed from the crystal structure. It has a central pore of approximately 4-5 A radius, a size sufficient to enable transport of ions, with a constricted region at one end, formed by a ring of Gln6 residues. Electrostatic calculations are consistent with it being a cationic channel.

Acetonitriles↗

PubMed2001

Peptaibols: models for ion channels.

Peptaibols are membrane-active polypeptides isolated from fungal sources. They are characterized by the presence of an unusual amino acid, alpha-aminoisobutyric acid, and a C-terminal hydroxylated amino acid. Peptaibols exhibit antibiotic activity against bacteria and fungi. Their amphipathic nature allows them to self-associate into oligomeric ion-channel assemblies which span the width of lipid bilayer membranes. Over 200 peptaibol sequences have been reported to date, which are compiled in the Peptaibol Database at http://www.cryst.bbk.ac.uk/peptaibol. Alignments of these sequences have been carried out in order to define a series of related subfamilies (SFs) with common sequence features thought to be important for channel formation. Crystal structures determined for a number of peptaibols from the various SFs provide the bases both for modelling of the channel structures and for modelling structures of other members of the same SFs.

Alamethicin↗

PubMedDate not supplied

The peptaibol database: a sequence and structure resource.

The peptaibols are a large family of membrane-active peptides with considerable sequence homology, but with different biological properties and three-dimensional structures. They constitute a rich resource of naturally occurring 'mutants' which are potentially valuable for structure/function studies of ion channels. A searchable on-line database of sequences and structures of the peptaibols has been created at http://www.cryst.bbk.ac.uk/peptaibol, as a resource for the biological and structural community. In this paper, the contents and organization of the website are discussed as well as procedures for submission of new entries to the database. At present, more than 300 peptaibol sequences are stored in the database. Each sequence entry contains its full literature reference and information about its biological source. Tools are provided for searching for specific peptaibol sequences or groupings of sequences, and for locating peptaibols containing specified sequence motifs. In addition the website acts as a database for structural information. The coordinates of all currently available peptaibol x-ray and NMR structures are included and complemented, where appropriate. with molecular graphics illustrations. These include figures of model channel structures and comparisons between different peptaibol structures. The peptaibol database thus provides a tool for ready access to information and a means of investigating the sequences and structures of this class of polypeptides.

Amino Acid Sequence↗