Right-handed DNA Supercoiling by an Octameric Form of Histone-like Protein HU

In bacteria, the contribution of global nucleoid organization in determining cellular transcription programs is unclear. Using a mutant form of the most abundant nucleoid-associated protein HU, HUalpha(E38K,V42L), we previously showed that nucleoid remodeling by the mutant protein re-organizes the global transcription pattern. Here, we demonstrate that, unlike the dimeric wild-type HU, HUalpha(E38K,V42L) is an octamer and wraps DNA around its surface. The formation of wrapped nucleoprotein complexes by HUalpha(E38K,V42L) leads to a high degree of DNA condensation. The DNA wrapping is right-handed, which restrains positive supercoils. In vivo, HUalpha(E38K,V42L) shows altered association and distribution patterns with the genetic loci whose transcription are differentially affected in the mutant strain.

Folding and assembly pathways of co-chaperonin proteins 10: Origin of bacterial thermostability

To compare folding/assembly processes of heptameric co-chaperonin proteins 10 (cpn10) from different species and search for the origin of thermostability in hyper-thermostable Aquifex aeolicus cpn10 (Aacpn10), we have studied two bacterial variants-Aacpn10 and Escherichia coli cpn10 (GroES)-and compared the results to data on Homo sapiens cpn10 (hmcpn10). Equilibrium denaturation of GroES by urea, guanidine hydrochloride (GuHCl) and temperature results in coupled heptamer-to-monomer transitions in all cases. This is similar to the behavior of Aacpn10 but differs from hmcpn10 denaturation in urea. Time-resolved experiments reveal that GroES unfolds before heptamer dissociation, whereas refolding/reassembly begins with folding of individual monomers; these assemble in a slower step. The sequential folding/assembly mechanism for GroES is rather similar to that observed for Aacpn10 but contradicts the parallel paths of hmcpn10. We reveal that Aacpn10's stability profile is shifted upwards, broadened, and also moved horizontally to higher temperatures, as compared to that of GroES.

Articular cartilage collagen: an irreplaceable framework?

Adult articular cartilage by dry weight is two-thirds collagen. The collagen has a unique molecular phenotype. The nascent type II collagen fibril is a heteropolymer, with collagen IX molecules covalently linked to the surface and collagen XI forming the filamentous template of the fibril as a whole. The functions of collagens IX and XI in the heteropolymer are far from clear but, evidently, they are critically important since mutations in COLIX and COLXI genes can result in chondrodysplasia syndromes. Here we review what is known of the collagen assembly and present new evidence that collagen type III becomes covalently added to the polymeric fabric of adult human articular cartilage, perhaps as part of a matrix repair or remodelling process.

Amino-terminal domain stability mediates apolipoprotein E aggregation into neurotoxic fibrils

The three isoforms of apolipoprotein (apo) E are strongly associated with different risks for Alzheimer's disease: apoE4>apoE3>apoE2. Here, we show at physiological salt concentrations and pH that native tetramers of apoE form soluble aggregates in vitro that bind the amyloid dyes thioflavin T and Congo red. However, unlike classic amyloid fibrils, the aggregates adopt an irregular protofilament-like morphology and are seemingly highly alpha-helical. The aggregates formed at substantially different rates (apoE4>apoE3>apoE2) and were significantly more toxic to cultured neuronal cells than the tetramer. Since the three isoforms have large differences in conformational stability that can influence aggregation and amyloid pathways, we tested the effects of mutations that increased or decreased stability. Decreasing the conformational stability of the amino-terminal domain of apoE increased aggregation rates and vice versa. Our findings provide a new perspective for an isoform-specific pathogenic role for apoE aggregation in which differences in the conformational stability of the amino-terminal domain mediate neurodegeneration.

Plasma membrane calcium pumps in mouse olfactory sensory neurons

We report here the presence of specific plasma membrane calcium pumps (PMCAs) in mouse olfactory sensory neurons. All 4 isoforms are present as shown by deconvolution microscopy, and the specific splice variants are identified by reverse transcriptase (RT)-polymerase chain reaction (PCR). The PMCAs are present on the cell body, dendrite, knob, and cilia, but the different isoforms of PMCAs are not identical in their distributions. The PMCAs are positioned to play a role in calcium clearance after stimulation.

Formation of soluble oligomers and amyloid fibrils with physical properties of the scrapie isoform of the prion protein from the C-terminal domain of recombinant murine prion protein mPrP-(121-231)

Prion diseases are fatal neurodegenerative disorders associated with conformational conversion of the cellular prion protein, PrP(C), into a misfolded, protease-resistant form, PrP(Sc). Here we show, for the first time, the oligomerization and fibrillization of the C-terminal domain of murine PrP, mPrP-(121-231), which lacks the entire unstructured N-terminal domain of the protein. In particular, the construct we used lacks amino acid residues 106-120 from the so-called amyloidogenic core of PrP (residues 106-126). Amyloid formation was accompanied by acquisition of resistance to proteinase K digestion. Aggregation of mPrP-(121-231) was investigated using a combination of biophysical and biochemical techniques at pH 4.0, 5.5, and 7.0 and at 37 and 65 degrees C. Under partially denaturing conditions (65 degrees C), aggregates of different morphologies ranging from soluble oligomers to mature amyloid fibrils of mPrP-(121-231) were formed. Transmission electron microscopy analysis showed that roughly spherical aggregates were readily formed when the protein was incubated at pH 5.5 and 65 degrees C for 1 h, whereas prolonged incubation led to the formation of mature amyloid fibrils. Samples incubated at 65 degrees C at pH 4.0 or 7.0 presented an initial mixture of oligomers and protofibrils or fibrils. Electrophoretic analysis of samples incubated at 65 degrees C revealed formation of sodium dodecyl sulfate-resistant oligomers (dimers, trimers, and tetramers) and higher molecular weight aggregates of mPrP-(121-231). These results demonstrate that formation of an amyloid form with physical properties of PrP(Sc) can be achieved in the absence of the flexible N-terminal domain and, in particular, of residues 106-120 of PrP and does not require other cellular factors or a PrP(Sc) template.

Multiple isoforms of myosin light chain 1 in pig diaphragm slow fibers: correlation with maximal shortening velocity and force generation

Pig diaphragm slow fibers exhibit heterogeneity in myosin light chain 1 (MLC1) isoform expression, with many expressing fast-type MLC1 (MLC1F), as well as two isoforms of slow-type MLC1 (MLC1Sa and MLC1Sb). The goal of this study was to test if there is a relationship between MLC1 isoform expression and contractile properties among these fibers. Maximal shortening velocity (V(max)) and maximal isometric force generation, normalized with fiber cross-sectional area (P(o)/CSA), were measured in single fibers. V(max) was inversely related to the relative level of MLC1Sa. The level of MLC1Sa was reciprocally related to the levels of MLC1Sb and of MLC1F among individual fibers. Fibers expressing MLC1Sa and in which MLC1Sb was not detected generated greater P(o)/CSA, compared to fibers expressing MLC1Sb and not MLC1Sa. The results indicate a complex pattern of MLC1 isoform expression among pig diaphragm slow fibers and suggest that shortening velocity and force generation are modulated, in these fibers, by the MLC1 isoform composition.

Quaternary polymorphism of replicative helicase G40P: structural mapping and domain rearrangement

Quaternary polymorphism is a distinctive structural feature of the DnaB family of replicative DNA hexameric helicases. The Bacillus subtilis bacteriophage SPP1 gene 40 product (G40P) belongs to this family. Three different quaternary states have been described for G40P homohexamers, two of them with C(3) symmetry, and the other with C(6) symmetry. We present three-dimensional reconstructions of the different architectures of G40P hexamers and a variant lacking the N-terminal domain. Comparison of the G40P and the deletion mutant structures sheds new light on the functional roles of the N and C-terminal domains, at the same time that it allows the direct structural mapping of these domains. Based on this new information, hybrid EM/X-ray models are presented for all the different symmetries. These results suggest that quaternary polymorphism of hexameric helicases may be implicated in the translocation along the DNA.

Molecular characterization and immunohistochemical localization of palmdelphin, a cytosolic isoform of the paralemmin protein family implicated in membrane dynamics

Palmdelphin is a newly identified cytosolic isoform of paralemmin-1, a lipid raft-associated protein implicated in cell shape control. Like paralemmin-1, palmdelphin is phosphorylated, giving rise to electrophoretic band heterogeneity that is most pronounced in the brain. In ultracentrifugation and gel filtration palmdelphin behaves as a non-globular monomer. Its C-terminal region binds glutamine synthetase. Immunohistochemical analysis of the rat brain shows a prominent localization of palmdelphin in the cerebral cortex, hippocampus, amygdala, septum, indusium griseum, piriform cortex, nucleus supraopticus, and nucleus of the lateral olfactory tract. Many of the circumscript palmdelphin-positive areas are related to the olfactory system. Immunoperoxidase electron microscopy reveals a discontinuous distribution of palmdelphin immunoreactivity, in the form of spots scattered throughout the cytoplasm of selected neuronal perikarya and dendrites, including dendritic spines, often in association with endomembranes, and in a pattern which is similar to that of the cytoplasmic fraction of paralemmin-1. In subcellular fractionation experiments palmdelphin behaves as a cytosolic protein which, however, can be partially recruited from cytosol to the detergent-resistant fraction of a membrane/cytoskeletal cell ghost preparation. These observations suggest that palmdelphin may peripherally associate with endomembranes or cytoskeleton-linked structures.

Rapana thomasiana hemocyanin (RtH): comparison of the two isoforms, RtH1 and RtH2, at 19A and 16A resolution

Three-dimensional (3D) reconstructions of the two 8.4 MDa Rapana thomasiana hemocyanin isoforms, RtH1 and RtH2, have been obtained by cryoelectron microscopy of molecules embedded in vitreous ice and single particle image processing. The final 3D structures of the RtH1 and RtH2 didecamers at 19 A and 16 A resolution, respectively, are very similar to earlier reconstructions of gastropodan hemocyanins, revealing structural features such as the obliquely oriented subunits, the five- and two-fold symmetrical axes. Three new interactions are defined; two of them connecting the arch and the wall while the third is formed between the collar and the wall. The collar-wall connection and one of the arch-wall connections are positioned between two individual subunit dimers, while the second arch-wall connection is located between two subunits within the subunit dimer. All three interactions establish connections to the first tier of the wall. Furthermore, for each interaction we have allocated two first tier functional units most likely involved in forming the connections.

Assembly of the full-length recombinant mouse prion protein I. Formation of soluble oligomers

The conversion of a monomeric alpha-helix-rich isoform to multimeric beta-sheet-rich isoforms is a prominent feature of the conversion between PrP(C) and PrP(SC). We mimicked this process in vitro by exposing an unglycosylated recombinant form of the full-length mouse prion protein ((Mo)PrP(23-231)) to an acidic pH, at 37 degrees C, and we monitored the kinetics of conformational change and assembly. In these conditions, monomeric (Mo)PrP(23-231) converts slowly to two ensembles of soluble oligomers that are separated by size exclusion chromatography. The larger oligomers (I) are unstable, and their formation involves almost no change in secondary structure content. The smaller oligomers (II) form stable spherical or annular particles containing between 8 and 15 monomers as determined by multi-angle laser light scattering (MALLS). Their formation is concomitant with the main, thought limited, change in the secondary structure content (10%) seen by Fourier Transform Infrared (FTIR) spectroscopy. Even if these oligomers conserve a large part of the secondary structure of monomeric PrP, they exhibit amyloid features with the appearance of intermolecular beta-structure as revealed by the appearance of an IR band below 1620 cm(-1).

Production and characterization of astrocyte-derived human apolipoprotein E isoforms from immortalized astrocytes and their interactions with amyloid-beta

The apolipoprotein E (apoE) genotype is an important genetic risk factor for Alzheimer's disease (AD). In the central nervous system (CNS), most apoE is produced by astrocytes and is present in unique high-density lipoprotein (HDL)-like particles that have distinct properties from apoE derived from other sources. To develop an efficient system to produce astrocyte-derived apoE in large quantities, we produced and characterized immortalized cell lines from primary astrocyte cultures derived from human APOE knock-in mice. APOE2, APOE3, and APOE4 expressing cell lines were established that secrete apoE in HDL-like particles at similar levels, cholesterol composition, and size as those produced by primary astrocytes. In physiological buffers, astrocyte-secreted apoE3 and E4 associated equally well with amyloid-beta. Under the same conditions, only a small fraction of A beta formed sodium dodecyl sulfate (SDS)-stable complexes with apoE (E3 > E4). These immortalized astrocytes will be useful for studying mechanisms underlying the isoform-specific effects of apoE in the CNS.

In Vitro Conversion of Mammalian Prion Protein into Amyloid Fibrils Displays Unusual Features†

The "protein only" hypothesis of prion propagation postulates that the abnormal isoform of the prion protein, PrP(Sc), acts as a causative and transmissible agent of prion disease. In attempt to reconstitute prion infectivity in vitro, we previously developed a cell-free conversion protocol for generating amyloid fibrils from a recombinant prion protein encompassing residues 89-231 (rPrP 89-230) [Baskakov et al. (2002) J. Biol. Chem. 277, 21140]. When inoculated into transgenic mice, these amyloid fibrils induced prion disease, which can be efficiently transmitted to both wild-type and transgenic mice [Legname et al. (2004) Science 305, 673]. Here we show that the polymerization of rPrPs into the fibrils displays a number of distinctive kinetic features that are not typical for polymerization by other amyloidogenic polypeptides. Specifically, the lag phase of polymerization showed only modest dependence on protein concentration, and the conversion reaction displayed a dramatic volume-dependent threshold effect. To explain these unique kinetic features, we proposed that the conversion reaction is regulated by the dynamics between the rates of multiplication and deactivation of self-propagating fibrillar isoforms. Our further studies demonstrated that surface-dependent sorption of fibrillar isoforms is responsible for their deactivation in vitro, while fibril fragmentation seems to account for the multiplication of the active centers of polymerization. Our findings support the hypothesis that development of prion disease is controlled by a fine dynamic balance between self-propagation and clearance/deactivation of PrP(Sc).

Sorting of a nonmuscle tropomyosin to a novel cytoskeletal compartment in skeletal muscle results in muscular dystrophy

Tropomyosin (Tm) is a key component of the actin cytoskeleton and >40 isoforms have been described in mammals. In addition to the isoforms in the sarcomere, we now report the existence of two nonsarcomeric (NS) isoforms in skeletal muscle. These isoforms are excluded from the thin filament of the sarcomere and are localized to a novel Z-line adjacent structure. Immunostained cross sections indicate that one Tm defines a Z-line adjacent structure common to all myofibers, whereas the second Tm defines a spatially distinct structure unique to muscles that undergo chronic or repetitive contractions. When a Tm (Tm3) that is normally absent from muscle was expressed in mice it became associated with the Z-line adjacent structure. These mice display a muscular dystrophy and ragged-red fiber phenotype, suggestive of disruption of the membrane-associated cytoskeletal network. Our findings raise the possibility that mutations in these tropomyosin and these structures may underpin these types of myopathies.

Molecular identification of a calcium-inhibited catalytic subunit of casein kinase type 2 from Paramecium tetraurelia

We have previously described the occurrence in Paramecium of a casein kinase (CK) activity (EC 2.7.1.37) with some unusual properties, including inhibition by Ca(2+) (R. Kissmehl, T. Treptau, K. Hauser, and H. Plattner, FEBS Lett. 402:227-235, 1995). We now have cloned four genes, PtCK2alpha1 to PtCK2alpha4, all of which encode the catalytic alpha subunit of type 2 CK (CK2) with calculated molecular masses ranging from 38.9 to 39.4 kDa and pI values ranging from 8.8 to 9.0. They can be classified into two groups, which differ from each other by 28% on the nucleotide level and by 18% on the derived amino acid level. One of them, PtCK2alpha3, has been expressed in Escherichia coli and characterized in vitro. As we also have observed with the isolated CK, the recombinant protein preferentially phosphorylates casein but also phosphorylates some Paramecium-specific substrates, including the exocytosis-sensitive phosphoprotein pp63/parafusin. Characteristically, Ca(2+) inhibits the phosphorylation at elevated concentrations occurring during stimulation of a cell. Reconstitution with a recombinant form of the regulatory subunit from Xenopus laevis, XlCK2beta, confirms Ca(2+) sensitivity also under conditions of autophosphorylation. This is unusual for CK2 but correlates with the presence of two EF-hand calcium-binding motifs, one of which is located in the N-terminal segment essential for constitutive activity, as well as with an aberrant composition of normally basic domains recognizing acidic substrate domains. Immunogold localization reveals a considerable enrichment in the outermost cell cortex layers, excluding cilia. We discuss a potential role of this Ca(2+)-inhibited PtCK2alpha species in a late step of signal transduction.

Ligand-dependent inhibition and reversal of tau filament formation

Alzheimer's disease is defined in part by the intraneuronal accumulation of filaments comprised of the microtubule associated protein tau. Because animal model studies suggest that a toxic gain of function accompanies tau aggregation in neurons, selective pharmacological inhibitors of the process may have utility in slowing neurodegeneration. Here, the properties of a candidate small molecule inhibitor of tau fibrillization, 3-(2-hydroxyethyl)-2-[2-[[3-(2-hydroxyethyl)-5-methoxy-2-benzothiazolylidene]methyl]-1-butenyl]-5-methoxybenzothiazolium (N744), were characterized in vitro using transmission electron microscopy. N744 inhibited arachidonic acid-induced aggregation of full-length, four-repeat tau protein at substoichiometric concentrations relative to total tau and with an IC(50) of approximately 300 nM. Inhibition was accompanied by a dose-dependent decrease in the number concentration of filaments, suggesting that N744 interfered with tau filament nucleation. Stoichiometric concentrations of N744 also promoted tau disaggregation when added to mature synthetic filaments. Disaggregation followed first-order kinetics and was accompanied by a steady decrease in filament number, suggesting that N744 promoted endwise loss of tau molecules with limited filament breakage. N744 at substoichiometric concentrations did not inhibit Abeta and alpha-synuclein aggregation, indicating it was tau selective under these conditions. Because of its activity in vitro, N744 may offer a pharmacological approach to the role of tau fibrillization in neurodegeneration.

Tau paired helical filaments from Alzheimer's disease brain and assembled in vitro are based on beta-structure in the core domain

Tau protein, a neuronal microtubule-associated protein, forms insoluble fibers ("paired helical filaments") in Alzheimer's disease and other tauopathies. Conflicting views on the structure of the fibers have been proposed recently, ranging from mainly alpha-helical structure to mainly beta-sheet, or a mixture of mostly random coil and beta-sheet. We have addressed this issue by studying tau fibers immunopurified from Alzheimer brain tissue by a conformation-specific antibody and comparing them with fibers reassembled from recombinant tau or tau constructs in vitro, using a combination of electron microscopy and spectroscopic methods. Brain-derived fibers and reassembled fibers both exhibit a typical twisted appearance when examined by electron microscopy. The soluble tau protein is a natively unfolded protein dominated by random coil structure, whereas Alzheimer PHFs and reassembled fibers show a shift toward an increase in the level of beta-structure. The results support a model in which the repeat domain of tau (which lies within the core of PHFs) adopts an increasing level of beta-structure during aggregation, whereas the N- and C-terminal domains projecting away from the PHF core are mostly random coil.

Lipid-binding studies of human apolipoprotein A-I and its terminally truncated mutants

Apolipoprotein A-I (apoA-I, 243 amino acids) is the major protein of high-density lipoproteins (HDL) that plays an important structural and functional role in lipid transport and metabolism. The central region of apoA-I (residues 60-183) is predicted to contain exclusively amphipathic alpha-helices formed from tandem 22-mer sequence repeats. To analyze the lipid-binding properties of this core domain, four terminally truncated mutants of apoA-I, Delta(1-41), Delta(1-59), Delta(1-41,185-243), and Delta(1-59,185-243), were expressed in baculovirus infected Sf-9 cells. The effects of mutations on the ability of apoA-I to form bilayer disk complexes with dimyristoyl phosphatidylcholine (DMPC) that resemble nascent HDL were analyzed by density gradient ultracentrifugation and electron microscopy (EM). The N-terminal deletion mutants, Delta(1-41) and Delta(1-59), showed altered lipid-binding ability as compared to plasma and wild-type apoA-I, and in the double deletion mutants, Delta(1-41, 185-243) and Delta(1-59, 185-243), the lipid binding was abolished. Thermal unfolding of variant apoA-I/DMPC complexes monitored by circular dichroism (CD) showed hysteresis and a shift in the melting curves by about -12 degrees C upon reduction in the heating rate from 1.0 to 0.067 K/min. This indicates an irreversible kinetically controlled transition with a high activation energy E(a) = 60 +/- 5 kcal/mol. CD and EM studies of the apoA-I/DMPC complexes at different pH demonstrated that changes in the net charge or in the charge distribution on the apoA-I molecule have critical effects on the conformation and lipid-binding ability of the protein.

Differential expression of p120 catenin in glial cells of the adult rat brain

p120 catenin (p120ctn) is involved in the regulation of cadherin-mediated adhesion and the dynamic organization of the actin cytoskeleton by modulating RhoGTPase activity. We have previously described the distribution of p120ctn during rat brain development and provided substantial evidence for the potential involvement of p120ctn in morphogenetic events and plasticity in the central nervous system. Here, we analyzed the cellular and ultrastructural distribution of p120ctn in glial cells of the adult rat forebrain. The highest intensity of immunostaining for p120ctn was found in cells of the choroid plexus and ependyma and was mainly restricted to the plasma membrane. However, p120ctn was almost absent from astrocytes. In contrast, in tanycytes, a particular glial cell exhibiting remarkable morphological plasticity, p120ctn, was localized at the plasma membrane and also in the cytoplasm. We show that a large subpopulation of oligodendrocytes expressed multiple isoforms, whereas other neural cells predominantly expressed isoform 1, and that p120ctn immunoreactivity was distributed through the cytoplasm and at certain portions of the plasma membrane. Finally, p120ctn was expressed by a small population of cortical NG2-expressing cells, whereas it was expressed by a large population of these cells in the white matter. However, in both regions, proliferating NG2-positive cells consistently expressed p120ctn. The expression of p120ctn by cells of the oligodendrocyte lineage suggests that p120ctn may participate in oligodendrogenesis and myelination. Moreover, the expression of p120ctn by various cell types and its differential subcellular distribution strongly suggest that p120ctn may serve multiple functions in the central nervous system.

NCAM180 and glutamate receptor subtypes in potentiated spine synapses: an immunogold electron microscopic study

Activity-dependent changes in expression and localization of the largest major isoform of the neural cell adhesion molecule NCAM180 and three subtypes of glutamate receptors predominantly expressed in the outer part of the molecular layer of the dentate gyrus of adult rats-the NMDA receptor NR2A, the AMPA receptor GluR2/3, and the metabotropic glutamate receptor mGluR1 - were investigated using postembedding immunogold labeling, and electron microscopy. In synaptic membranes of nonstimulated spine synapses, NCAM180 and NR2A accumulated in the center of the postsynaptic density, whereas GluR2/3 and mGluR1 were distributed evenly. Twenty-four hours following induction of long-term potentiation in vivo, NCAM180 and NR2A accumulated at the edges of postsynaptic densities, whereas GluR2/3 was localized more centrally. Also, the distribution of gold particles per synapse significantly changed for NCAM180, NR2A, and mGluR1. Thus, changes in synaptic strength are associated with concomitant changes in the expression and distribution of NCAM180 and glutamate receptors, particularly of the NR2A subtype.

BPAG1n4 is essential for retrograde axonal transport in sensory neurons

Disruption of the BPAG1 (bullous pemphigoid antigen 1) gene results in progressive deterioration in motor function and devastating sensory neurodegeneration in the null mice. We have previously demonstrated that BPAG1n1 and BPAG1n3 play important roles in organizing cytoskeletal networks in vivo. Here, we characterize functions of a novel BPAG1 neuronal isoform, BPAG1n4. Results obtained from yeast two-hybrid screening, blot overlay binding assays, and coimmunoprecipitations demonstrate that BPAG1n4 interacts directly with dynactin p150Glued through its unique ezrin/radixin/moesin domain. Studies using double immunofluorescent microscopy and ultrastructural analysis reveal physiological colocalization of BPAG1n4 with dynactin/dynein. Disruption of the interaction between BPAG1n4 and dynactin results in severe defects in retrograde axonal transport. We conclude that BPAG1n4 plays an essential role in retrograde axonal transport in sensory neurons. These findings might advance our understanding of pathogenesis of axonal degeneration and neuronal death.

Titin as a modular spring: emerging mechanisms for elasticity control by titin in cardiac physiology and pathophysiology

Titin is a giant elastic protein that functions as a molecular spring that develops passive muscle stiffness. Here we discuss the molecular basis of titin's extensibility, how titin's contribution to passive muscle stiffness may be adjusted and how adjustment of titin's stiffness may influence muscle contraction. We also focus on ligands that link titin to membrane channel activity, protein turnover and gene expression.

Stretching and visualizing titin molecules: combining structure, dynamics and mechanics

The details of the global and local structure and function of titin, a giant filamentous intrasarcomeric protein are largely undiscovered. Here we discuss a combination of bulk-solution and novel single-molecule techniques that may lend unique insights into titin's molecular dynamic, structural and mechanical characteristics.