Rolf Misselwitz

Bio: Rolf Misselwitz is an academic researcher from Max Delbrück Center for Molecular Medicine. The author has contributed to research in topics: Circular dichroism & Radius of gyration. The author has an hindex of 22, co-authored 41 publications receiving 1156 citations.

Compactness of protein molten globules : temperature-induced structural changes of the apomyoglobin folding intermediate

Abstract: Apomyoglobin undergoes a two-step unfolding transition when the pH is lowered from 6 to 2. The partly folded intermediate (1) state at pH 4 and low ionic strength has properties of a molten globule. We have studied structural features of this state, its compactness, content of secondary structure, and specific packing of aromatic side chains, using dynamic light scattering, and small-angle X-ray scattering and far- and near-ultraviolet circular dichroism spectroscopy. Particular attention was paid to temperature-dependent structural changes. The results are discussed with reference to the native-like (N) state and the highly unfolded (U) state. It turned out that the I-state is most compact near 30°C, having a Stokes radius 20% larger and a radius of gyration 30% larger than those of the N-state. Both cooling and heating relative to 30°C led to an expansion of the molecule, but the structural changes at low and high temperatures were of a different kind. At temperatures above 40°C non co-operative melting of structural elements was observed, while the secondary structure was essentially retained on cooling. The results are discussed in context with theoretical predictions of the compactness and the stability of apomyoglobin by Alonso et al. [Alonso, D. O. V., Dill, K, A., and Stigler, D. (1991) Biopolymers 31:1631–1649]. Comparing the I-state of apomyoglobin with the molten globules of α-lactalbumin and cytochrome c, we found that the compactness of the molten globule states of the three proteins decreases in the order α-lactalbumin > apocytochrome c > apomyoglobin. While α-lactalbumin and cytochrome c are rather homogeneously expanded, apomyoglobin exhibits a non uniform expansion, since two structural domains could clearly be detected by small-angle X-ray scattering.

Secondary structure of streptokinase in aqueous solution: a Fourier transform infrared spectroscopic study.

Abstract: The secondary structure of streptokinase (Sk) in aqueous solution was quantitatively examined by using Fourier transform infrared (FT-IR) spectroscopy. Resolution enhancement techniques, including Fourier deconvolution and derivative spectroscopy, were combined with band curve-fitting procedures to quantitate the spectral information from the amide I bands. Nine component bands were found under the broad, nearly featureless amide I bands which reflect the presence of various substructures. The relative areas of these component bands indicate an amount of beta-sheet between 30 and 37% and an alpha-helix content of only 12-13% in Sk. Further conformational substructures are assigned to turns (25-26%) and to "random" structures (15-16%). Additionally, the correlation of a pronounced component band near 1640 cm-1 (10-16% fractional area) with the possible presence of 3(10)-helices is discussed.

Cold denaturation-induced conformational changes in phosphoglycerate kinase from yeast

Abstract: The temperature-dependent conformational equilibrium of 3-phosphoglycerate kinase has been studied in the temperature range from 1 to 30 degrees C by means of dynamic light scattering, small-angle X-ray scattering, differential scanning calorimetry, circular dichroism spectroscopy, and fluorescence spectroscopy. At 28 degrees C and in the presence of 0.7 M guanidine hydrochloride (GuHCl), the radius of gyration (RG) and the Stokes radius (RS) are 2.44 and 3.09 nm, respectively. Decreasing the temperature effects unfolding of the molecule, a process that involves two stages. The two stages correspond to the successive unfolding of the N-terminal and C-terminal domains. The peak maxima of the excess heat capacity, determined from differential calorimetric scans, extrapolated to 0 scan rate, are positioned at 16.5 degrees C for the N-terminal domain and at 6.3 degrees C for the C-terminal domain. At 4.5 degrees C, the radius of gyration and the Stokes radius increase to 7.8 and 4.8 nm, respectively. The persistence length and the length of the statistical chain segment of the unfolded polypeptide chain are 1.74 and 3.48 nm, corresponding to five and ten amino acids, respectively. At 1 degrees C, the dimensions of the unfolded chain nearly agree with the predicted dimensions under theta conditions. Thus, the conformational changes upon cold denaturation can be described by a transition from a compactly folded molecule to a random coil. The conformation-dependent ratio rho = RGRS-1 increases from rho = 0.79 to rho = 1.63. The volume of the unfolded chain is 30 times larger than that of the folded chain in the native state.(ABSTRACT TRUNCATED AT 250 WORDS)

In vitro and in vivo stability of the epsilon2zeta2 protein complex of the broad host-range Streptococcus pyogenes pSM19035 addiction system.

Abstract: Streptococcus pyogenes pSM19035-encoded epsilon (10.7 kDa) and zeta (32.4 kDa) proteins are necessary to secure stable plasmid inheritance in bacteria, with zeta acting as toxin that kills plasmid-deprived cells and epsilon as an antitoxin that neutralises the activity of zeta. The epsilon and zeta proteins co-purify as a stable complex that, according to analytical ultracentrifugation and gel filtration, exists as epsilon2zeta2 heterotetramer in solution. Co-crystals of the epsilon2zeta2 complex contain epsilon and zeta in 1:1 molar ratio. Unfolding studies monitoring circular dichroic and fluorescence changes show that the zeta protein has a significantly lower thermodynamic stability than the epsilon protein both in free state and in the complex. Proteolytic studies indicate that zeta protein is more stable in the epsilon2zeta2 complex than in the free state. In vivo studies reveal a short half-life of the epsilon antitoxin (-18 min) and a long lifetime of the zeta toxin (>60 min). When transcription-translation of a plasmid containing the epsilon and zeta genes was inhibited, cell death was observed after a short lag phase that correlates with the disappearance of the epsilon protein from the background.

The microglia-activating potential of thrombin: the protease is not involved in the induction of proinflammatory cytokines and chemokines.

Abstract: The serine protease thrombin is known as a blood coagulation factor. Through limited cleavage of proteinase-activated receptors it can also control growth and functions in various cell types, including neurons, astrocytes, and microglia (brain macrophages). A number of previous studies indicated that thrombin induces the release of proinflammatory cytokines and chemokines from microglial cells, suggesting another important role for the protease beyond hemostasis. In the present report, we provide evidence that this effect is not mediated by any proteolytic or non-proteolytic mechanism involving thrombin proper. Inhibition of the enzymatic thrombin activity did not affect the microglial release response. Instead the cyto-/chemokine-inducing activity solely resided in a high molecular weight protein fraction that could be isolated in trace amounts even from apparently homogenous α- and γ-thrombin preparations. High molecular weight material contained thrombin-derived peptides as revealed by mass spectrometry but was devoid of thrombin-like enzymatic activity. Separated from the high molecular weight fraction by fast protein liquid chromatography, enzymatically intact α- and γ-thrombin failed to trigger any release. Our findings may force a revision of the notion that thrombin itself is a direct proinflammatory release signal for microglia. In addition, they could be relevant for the study of other cellular activities and their assignment to this protease.

How to measure and predict the molar absorption coefficient of a protein.

Abstract: The molar absorption coefficient, E, of a protein is usually based on concentrations measured by dry weight, nitrogen, or amino acid analysis. The studies reported here suggest that the Edelhoch method is the best method for measuring E for a protein. (This method is described by Gill and von Hippel [1989, Anal Biochem 182:3193261 and is based on data from Edelhoch [1967, Biochemistry 6:1948-19541.) The absorbance of a protein at 280 nm depends on the content of Trp, Tyr, and cystine (disulfide bonds). The average E values for these chromophores in a sample of 18 well-characterized proteins have been estimated, and the E values in water, propanol, 6 M guanidine hydrochloride (GdnHCI), and 8 M urea have been measured. For Trp, the average E values for the proteins are less than the E values measured in any of the solvents. For Tyr, the average E values for the proteins are intermediate between those measured in 6 M GdnHCl and those measured in propanol. Based on a sample of 116 measured t values for 80 proteins, the t at 280 nm of a folded protein in water, t(280), can best be predicted with this equation:

Physiology of Microglia

Abstract: Microglial cells are the resident macrophages in the central nervous system. These cells of mesodermal/mesenchymal origin migrate into all regions of the central nervous system, disseminate through the brain parenchyma, and acquire a specific ramified morphological phenotype termed "resting microglia." Recent studies indicate that even in the normal brain, microglia have highly motile processes by which they scan their territorial domains. By a large number of signaling pathways they can communicate with macroglial cells and neurons and with cells of the immune system. Likewise, microglial cells express receptors classically described for brain-specific communication such as neurotransmitter receptors and those first discovered as immune cell-specific such as for cytokines. Microglial cells are considered the most susceptible sensors of brain pathology. Upon any detection of signs for brain lesions or nervous system dysfunction, microglial cells undergo a complex, multistage activation process that converts them into the "activated microglial cell." This cell form has the capacity to release a large number of substances that can act detrimental or beneficial for the surrounding cells. Activated microglial cells can migrate to the site of injury, proliferate, and phagocytose cells and cellular compartments.

Pathogenesis of Group A Streptococcal Infections

Abstract: Group A streptococci are model extracellular gram-positive pathogens responsible for pharyngitis, impetigo, rheumatic fever, and acute glomerulonephritis. A resurgence of invasive streptococcal diseases and rheumatic fever has appeared in outbreaks over the past 10 years, with a predominant M1 serotype as well as others identified with the outbreaks. emm (M protein) gene sequencing has changed serotyping, and new virulence genes and new virulence regulatory networks have been defined. The emm gene superfamily has expanded to include antiphagocytic molecules and immunoglobulin-binding proteins with common structural features. At least nine superantigens have been characterized, all of which may contribute to toxic streptococcal syndrome. An emerging theme is the dichotomy between skin and throat strains in their epidemiology and genetic makeup. Eleven adhesins have been reported, and surface plasmin-binding proteins have been defined. The strong resistance of the group A streptococcus to phagocytosis is related to factor H and fibrinogen binding by M protein and to disarming complement component C5a by the C5a peptidase. Molecular mimicry appears to play a role in autoimmune mechanisms involved in rheumatic fever, while nephritis strain-associated proteins may lead to immune-mediated acute glomerulonephritis. Vaccine strategies have focused on recombinant M protein and C5a peptidase vaccines, and mucosal vaccine delivery systems are under investigation.

Intrinsically Disordered Proteins

Abstract: Proteins can exist in a trinity of structures: the ordered state, the molten globule, and the random coil. The five following examples suggest that native protein structure can correspond to any of the three states (not just the ordered state) and that protein function can arise from any of the three states and their transitions. (1) In a process that likely mimics infection, fd phage converts from the ordered into the disordered molten globular state. (2) Nucleosome hyperacetylation is crucial to DNA replication and transcription; this chemical modification greatly increases the net negative charge of the nucleosome core particle. We propose that the increased charge imbalance promotes its conversion to a much less rigid form. (3) Clusterin contains an ordered domain and also a native molten globular region. The molten globular domain likely functions as a proteinaceous detergent for cell remodeling and removal of apoptotic debris. (4) In a critical signaling event, a helix in calcineurin becomes bound and surrounded by calmodulin, thereby turning on calcineurin's serine/threonine phosphatase activity. Locating the calcineurin helix within a region of disorder is essential for enabling calmodulin to surround its target upon binding. (5) Calsequestrin regulates calcium levels in the sarcoplasmic reticulum by binding approximately 50 ions/molecule. Disordered polyanion tails at the carboxy terminus bind many of these calcium ions, perhaps without adopting a unique structure. In addition to these examples, we will discuss 16 more proteins with native disorder. These disordered regions include molecular recognition domains, protein folding inhibitors, flexible linkers, entropic springs, entropic clocks, and entropic bristles. Motivated by such examples of intrinsic disorder, we are studying the relationships between amino acid sequence and order/disorder, and from this information we are predicting intrinsic order/disorder from amino acid sequence. The sequence-structure relationships indicate that disorder is an encoded property, and the predictions strongly suggest that proteins in nature are much richer in intrinsic disorder than are those in the Protein Data Bank. Recent predictions on 29 genomes indicate that proteins from eucaryotes apparently have more intrinsic disorder than those from either bacteria or archaea, with typically > 30% of eucaryotic proteins having disordered regions of length > or = 50 consecutive residues.

Principles of protein folding--a perspective from simple exact models.

Abstract: General principles of protein structure, stability, and folding kinetics have recently been explored in computer simulations of simple exact lattice models. These models represent protein chains at a rudimentary level, but they involve few parameters, approximations, or implicit biases, and they allow complete explorations of conformational and sequence spaces. Such simulations have resulted in testable predictions that are sometimes unanticipated: The folding code is mainly binary and delocalized throughout the amino acid sequence. The secondary and tertiary structures of a protein are specified mainly by the sequence of polar and nonpolar monomers. More specific interactions may refine the structure, rather than dominate the folding code. Simple exact models can account for the properties that characterize protein folding: two-state cooperativity, secondary and tertiary structures, and multistage folding kinetics-fast hydrophobic collapse followed by slower annealing. These studies suggest the possibility of creating "foldable" chain molecules other than proteins. The encoding of a unique compact chain conformation may not require amino acids; it may require only the ability to synthesize specific monomer sequences in which at least one monomer type is solvent-averse.