Transmembrane proteins are difficult to crystallize.
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Peer-reviewed literature and reference texts consistently report that transmembrane proteins are notoriously difficult to crystallize due to their physicochemical properties and amphipathic nature.
Structural Bioinformaticsmembrane proteinsenvironment-specific substitution tablesscoring matriceshomology recognitioncomparative modellingstructural lign nts r ctural gen ic initiatives a e expected to make 3D experimental data in the near future available for most proteins in nature. Yet, the class of transmembrane (TM) proteins represents a major obstacle to this goal. This is because their physicochemical properties make them extremely difficult to crystallize for X-ray crystallography studies, and hardly tractable for NMR spectroscopy experiments. Consequently, computational methods for predicting 3D structures are highly valuable. Comparative/ homology modelling remains the most effective approach to protein structure prediction [10]. This is because it takes advantage from already available experimental structural templates to build 3D models for a related protein of interest. Therefore the tools that search for structural templates need to be highly accurate. Many algorithms have been developed to increase the sensitivity and specificity of homology recognition for globular proteins, many of which exploit evolutionary and structural information [6]. However, they may not be generally applicable to TM proteins which have different structural features, amino acid composition and substitution rates. Thus, TM-specific algorithms are much needed. Our aim is to develop a sequence-structure homology recognition method that can use environmentspecific substitution tables and structure-dependent gap penalties [8] to (1) increase the accuracy of alignments involving TM protein sequences and structures and (2) improve the specificity and sensitivity of homology searches for TM proteins.
Crystallization and preliminary X-ray analysis of phosphoporin from the outer membrane of Escherichia coli.
Phosphoporin is a pore-forming transmembrane protein that spans the outer membrane of Escherichia coli and facilitates the diffusion of phosphates and phosphorylated compounds. Phosphoporin has been crystallized in several different crystal forms, although only one appears to be suitable for X-ray analysis. These crystals, which are hexagonal plates, diffract X-rays to 3 A resolution and belong to the space-group P6(3)22, with unit cell dimensions a = b = 121 A and c = 111 A.
Published in Journal of molecular biology (1991)
Three-dimensional crystals of an integral membrane protein: an initial x-ray analysis.
Matrix protein, a pore-forming transmembrane protein spanning the outer membrane of Escherichia coli, has been obtained in a variety of three-dimensional crystal forms amenable to both electron microscope and x-ray analyses. Successful association into large crystals depended on the use of alpha-octyl glucoside, a detergent with relatively low affinity for the protein. Electron micrographs of thin-sectioned crystals show a high degree of order. Preliminary crystallographic data suggest that the crystals, which exhibit diffraction to 3.8 A, have a cubic space group.
Published in The Journal of cell biology (1980)
Despite their functional relevance, little is known about the structures of the strongly hydrophobic transmembrane segments of integral membrane proteins such as the inhibitory glycine receptor [l].This receptor belongs to a class of topologically simple membrane proteins. It forms an anion channel due to the supramolecular association of five monomers, each consisting of four putative transmembrane segments Ml, M2, M3 and M4. M2 is unusually polar and thus thought to be involved in anion conduction. In order to span a membrane, the polar M2 would have to be stabilized by interacting with strongly nonpolar segments. Because it is difficult to crystallize membrane proteins for carrying out high resolution crystal structure determinations, alternative approaches employing for example spectroscopic methods need to be developed to obtain informations about structural features such as of single transmembrane segments.
3. 7. Transmembrane Protein Potential Membrane proteins are challenging to crystallize; therefore … they are more difficult to crystallize or their NMR spectra are difficult to resolve. Sequences … For example, multidomain proteins are often more difficult to express in bacterial host
antidepressants binding to their target proteins, the neurotransmitter transporters. As these proteins have proven difficult to be crystallized, LeuT emerged as
Bacterial Leucine Transporter (LeuT) is a bundled twelve alpha helix protein which belongs to the family of transporters that shuttle amino acids in and out of bacterial cells. Specialized in small hydrophobic amino acids such as leucine and alanine, this transporter is powered by the gradient of sodium ions that is normally maintained by healthy cells across their membranes. LeuT acts as a sympor
Bacterial Leucine Transporter (LeuT) is a bundled twelve alpha helix protein which belongs to the family of transporters that shuttle amino acids in and out of bacterial cells. Specialized in small hydrophobic amino acids such as leucine and alanine, this transporter is powered by the gradient of sodium ions that is normally maintained by healthy cells across their membranes. LeuT acts as a symporter, which means that it links the passage of a sodium ion across the cell membrane with the transport of the amino acid in the same direction. It was first crystallized to understand the inner molecular mechanisms of how antidepressants work, as it has a close resemblance with the human neurotransmitter transporters (more difficult to crystallize) that these drugs block, thus inhibiting the reuptake of chemical messengers across the cell membrane of nerve axons and glial cells.
Abstract Motivation: Residue–residue contacts across the transmembrane helices dictate the three-dimensional topology of alpha-helical membrane proteins. However, contact determination through experiments is difficult because most transmembrane proteins are hard to crystallize. Results: We present a novel method (MemBrain) to derive transmembrane inter-helix contacts from amino acid sequences by combining correlated mutations and multiple machine learning classifiers. Tested on 60 non-redundant polytopic proteins using a strict leave-one-out cross-validation protocol, MemBrain achieves an average accuracy of 62%, which is 12.5% higher than the current best method from the literature. When applied to 13 recently solved G protein-coupled receptors, the MemBrain contact predictions helped increase the TM-score of the I-TASSER models by 37% in the transmembrane region. The number of foldable cases (TM-score >0.5) increased by 100%, where all G protein-coupled receptor templates and homologous templates with sequence identity >30% were excluded. These results demonstrate significant progress in contact prediction and a potential for contact-driven structure modeling of transmembrane proteins. Availability: www.csbio.sjtu.edu.cn/bioinf/MemBrain/ Contact: hbshen@sjtu.edu.cn or zhng@umich.edu Supplementary information: Supplementary data are available at Bioinformatics online.
therefore notoriously difficult to crystallize. Membrane proteins are difficult to handle due to the amphipathic … likely to be optimal cases since these proteins are known to crystallize easily and to regularly produce large … crystallization method. Since membrane proteins are even more difficult to produce in large quantities than
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