Thermodynamic analysis reveals structural rearrangement during the acylation step in human trypsin 4 on 4-methylumbelliferyl 4-guanidinobenzoate substrate analogue.

Human trypsin 4 is an unconventional serine protease that possesses an arginine at position 193 in place of the highly conserved glycine. Although this single amino acid substitution does not affect steady-state activity on small synthetic substrates, it has dramatic effects on zymogen activation, interaction with canonical inhibitors, and substrate specificity toward macromolecular substrates. To study the effect of a non-glycine residue at position 193 on the mechanism of the individual enzymatic reaction steps, we expressed wild type human trypsin 4 and its R193G mutant. 4-Methylumbelliferyl 4-guanidinobenzoate has been chosen as a substrate analogue, where deacylation is rate-limiting, and transient kinetic methods were used to monitor the reactions. This experimental system allows for the separation of the individual reaction steps during substrate hydrolysis and the determination of their rate constants dependably. We suggest a refined model for the reaction mechanism, in which acylation is preceded by the reversible formation of the first tetrahedral intermediate. Furthermore, the thermodynamics of these steps were also investigated. The formation of the first tetrahedral intermediate is highly exothermic and accompanied by a large entropy decrease for the wild type enzyme, whereas the signs of the enthalpy and entropy changes are opposite and smaller for the R193G mutant. This difference in the energetic profiles indicates much more extended structural and/or dynamic rearrangements in the equilibrium step of the first tetrahedral intermediate formation in wild type human trypsin 4 than in the R193G mutant enzyme, which may contribute to the biological function of this protease

A fehérje-fehérje kölcsönhatások szerkezeti alapjai és biológiai szerepük: multidiszciplináris megközelítés = The structural basis and biological role of protein-protein interactions: a multidisciplinary approach

Az ELTE Biokémiai Tanszék tudományos kutatásainak tengelyében évtizedek óta a fehérjék szerkezetének, funkciójának és a fehérjék közötti kölcsönhatások szerkezeti hátterének és biológiai jelentőségének felderítése áll. Valamennyi, az elmúlt négyéves pályázati ciklusban vállalt feladatunk teljesítése a fenti célokat szolgálta. A vezető kutató megítélése szerint a pályázat támogatásával elért legkiemelkedőbb eredményeink, a vállalt témák sorrendjében a következők voltak: 1) Megállapítottuk, hogy a primata-specifikus tripszin 4 egyik, feltehetően biológiai szubsztrátja a mielin bázikus fehérje és modellt dolgoztunk ki a humán tripszinogén 4 asztroglia sejteken belüli transzportjának és aktivációjának követésére 2) Hazánkban elsőként állítottuk be a fágbemutatás módszerét, melynek segítségével az eredetitől eltérő specifitású proteáz inhibitorokat állítottunk elő. 3) Megállapítottuk, hogy a miozin II motorfehérje regulációs képességének az az előfeltétele, hogy aproximális kétláncú coiled-coil szerkezet instabil legyen. 4) Felderítettük a miozin II specifikus inhibitorának, a blebbistatinnak a működésmechanizmusát. 5) Kifejlesztettünk egy új tranziens kinetikai módszert, a ?temperature-jump/stopped flow-t a módszer alkalmazásához szükséges berendezéssel együtt. | For decades the focus of scientific interest of the Biochemistry Department, Eötvös Loránd University, Budapest has been the investigation of the structural basis and biological significance of protein-protein interactions. Our research efforts during the last 4 years were to achieve specific goals along this line. In the view of the principal investigator of this grant the most outstanding scientific results achieved, or discoveries made by using the financial means of the grant are as follows: 1) We provided indirect evidence that one of the potential pathological substrate of human trypsin 4 might be myelin basic protein. Furthermore, we worked out a model to follow the transport and activation of human trypsinogen 4 within human astroglia cells. 2) For the first time in Hungary we introduced the methodology of phage-display in our department and by using this method we succeeded in producing serine protease inhibitors with altered specificity. 3) Evidence was provided that the instability of the proximal two-chain coiled structure in myosin II plays an important regulatory role in the myosin functioning 4) The mechanism of action of the inhibitor of myosin II, blebbistatin was explored. 5) We developed and set up a new method and apparatus to perform ?temperature-jump/stopped flow? transient kinetics experiments

N-terminal regions of Mps1 kinase determine functional bifurcation

Spindle pole body components Spc29 and Cdc31 are identified as targets of Mps1 kinase, which, when phosphorylated, regulate protein–protein interactions in the spindle pole body

Phosphorylation of the yeast γ-tubulin Tub4 regulates microtubule function.

The yeast γ-tubulin Tub4 is assembled with Spc97 and Spc98 into the small Tub4 complex. The Tub4 complex binds via the receptor proteins Spc72 and Spc110 to the spindle pole body (SPB), the functional equivalent of the mammalian centrosome, where the Tub4 complex organizes cytoplasmic and nuclear microtubules. Little is known about the regulation of the Tub4 complex. Here, we isolated the Tub4 complex with the bound receptors from yeast cells. Analysis of the purified Tub4 complex by mass spectrometry identified more than 50 phosphorylation sites in Spc72, Spc97, Spc98, Spc110 and Tub4. To examine the functional relevance of the phosphorylation sites, phospho-mimicking and non-phosphorylatable mutations in Tub4, Spc97 and Spc98 were analyzed. Three phosphorylation sites in Tub4 were found to be critical for Tub4 stability and microtubule organization. One of the sites is highly conserved in γ-tubulins from yeast to human

Evolution of the diatoms: insights from fossil, biological and molecular data

Molecular sequence analyses have yielded many important insights into diatom evolution, but there have been few attempts to relate these to the extensive fossil record of diatoms, probably because of unfamiliarity with the data available, which are scattered widely through the geological literature. We review the main features of molecular phylogenies and concentrate on the correspondence between these and the fossil record; we also review the evolution of major morphological, cytological and life cycle characteristics, and possible diatom origins. The first physical remains of diatoms are from the Jurassic, and well-preserved, diverse floras are available from the Lower Cretaceous. Though these are unequivocally identifiable as centric diatoms, none except a possible Stephanopyxis can be unequivocally linked to lineages of extant diatoms, although it is almost certain that members of the Coscinodiscophyceae (radial centrics) and Mediophyceae (polar centrics) were present; some display curious morphological features that hint at an unorthodox cell division mechanism and life cycle. It seems most likely that the earliest diatoms were marine, but recently discovered fossil deposits hint that episodes of terrestrial colonization may have occurred in the Mesozoic, though the main invasion of freshwaters appears to have been delayed until the Cenozoic. By the Upper Cretaceous, many lineages are present that can be convincingly related to extant diatom taxa. Pennate diatoms appear in the late Cretaceous and raphid diatoms in the Palaeocene, though molecular phylogenies imply that raphid diatoms did in fact evolve considerably earlier. Recent evidence shows that diatoms are substantially underclassified at the species level, with many semicryptic or cryptic species to be recognized; however, there is little prospect of being able to discriminate between such taxa in fossil material