N-乙酰-L-半胱氨酸合成新工艺

研究了一步合成法生产 N-乙酰 -L-半胱氨酸的工艺 ,介绍了工艺过程并讨论了主要影响因素。该方法简单 ,操作方便 ,生产周期短 ,反应选择性好 ,产品得率及纯度很高 ,是一种具有应用价值的新方法     

Effect of stachydrine hydrochloride to the prostate hyperplasia model in mice

Study the effect of stachydrine hydrochloride to prostatic hyperplasia in mice which made of the urogenital sinus implantation. KM male mices were selected.The group was given the respective drugs for gavage, the group of BG and MG were given the distilled water which the same amount as the drugs group for 21 consecutive days. The level of DHT, ACP, Non PACP were measured in serum, the average wet weight of the prostate and prostate index were calculated, the expression of bFGF, EGF, IGF-I, TGF-β in prostate tissue were measured, the pathological changes of the prostate, kidney, thymus, spleen were observed by HE staining. Compared with MG, stachydrine hydrochloride high (SHH), medium (SHM) and low (SHL) group could reduced the level of DHT and PACP in serum significantly (P < 0.01); SHM and SHL could increased the express of TGF-β1 significantly (P < 0.05); SHH, SHM, SHL could reduced the express of EGF significantly (P < 0.01); SHM could reduced the express of IGF-Ⅰ significantly (P < 0.01); Compared with MG, SHH, SHM, SHL could reduced the pathological changes of prostate significantly (P < 0.01); FG could reduced the kidney pathological changes significantly (P < 0.01). Stachydrine hydrochloric had no significant effect on the kidney. Stachydrine hydrochloride had the effect of improve thymus, spleen pathological changes. Stachydrine hydrochloride has a good inhibition effect on prostatic hyperplasia model in mices.     

Investigation of the folding pathway of the TEM-1 β-lactamase

The TEM-1 β-lactamase is a globular protein containing 12 proline residues. The folding mechanism of this enzyme was investigated by kinetic and equilibrium experiments with the help of fluorescence spectroscopy and circular dichroism. The equilibrium denaturation of the protein induced by guanidine hydrochloride occurs in two discrete steps, indicating the existence of a thermodynamically stable intermediate state. Thisstate is 5.2 ± 0.4 kcal/mol less stable than the native conformation and 5.7 ± 0.2 kcal/mol more stable than the fully denaturedprotein. This intermediate state exhibits a high content of native secondary structure elements but is devoid of specific tertiary organization; its relation to the “molten globule” is discussed. Refolding kinetic experimentsrevealed the existence of a transient intermediate conformation between thethermodynamically stable intermediate and the native protein. This transient intermediate appears rapidly during the folding reaction. It exhibits a secondary structure content very similar to that of the native protein and has also recovered a significant amount of tertiary organisation. The final refolding step of the TEM-1 β-lactamase, leading to the native enzyme, is dominated by two major slow kinetic phases which probablyreflect a very complex process kinetically limited by proline cis/transisomerization. © 1995 Wiley-Liss, Inc.     

Cotranslational Folding Increases GFP Folding Yield

Protein sequences evolved to fold in cells, including cotranslational folding of nascent polypeptide chains during their synthesis by the ribosome. The vectorial (N- to C-terminal) nature of cotranslational folding constrains the conformations of the nascent polypeptide chain in a manner not experienced by full-length chains diluted out of denaturant. We are still discovering to what extent these constraints affect later, posttranslational folding events. Here we directly address whether conformational constraints imposed by cotranslational folding affect the partitioning between productive folding to the native structure versus aggregation. We isolated polyribosomes from Escherichia coli cells expressing GFP, analyzed the nascent chain length distribution to determine the number of nascent chains that were long enough to fold to the native fluorescent structure, and calculated the folding yield for these nascent chains upon ribosome release versus the folding yield of an equivalent concentration of full-length, chemically denatured GFP polypeptide chains. We find that the yield of native fluorescent GFP is dramatically higher upon ribosome release of nascent chains versus dilution of full-length chains from denaturant. For kinetically trapped native structures such as GFP, folding correctly the first time, immediately after release from the ribosome, can lead to lifelong population of the native structure, as opposed to aggregation.     

Insights from atomic-resolution X-ray structures of chemically synthesized HIV-1 protease in complex with inhibitors

The human immunodeficiency virus 1 (HIV-1) protease (PR) is an aspartyl protease essential for HIV-1 viral infectivity. HIV-1 PR has one catalytic site formed by the homodimeric enzyme. We chemically synthesized fully active HIV-1 PR using modern ligation methods. When complexed with the classic substrate-derived inhibitors JG-365 and MVT-101, the synthetic HIV-1 PR formed crystals that diffracted to 1.04- and 1.2-A resolution, respectively. These atomic-resolution structures revealed additional structural details of the HIV-1 PR's interactions with its active site ligands. Heptapeptide inhibitor JG-365, which has a hydroxyethylamine moiety in place of the scissile bond, binds in two equivalent antiparallel orientations within the catalytic groove, whereas the reduced isostere hexapeptide MVT-101 binds in a single orientation. When JG-365 was converted into the natural peptide substrate for molecular dynamic simulations, we found putative catalytically competent reactant states for both lytic water and direct nucleophilic attack mechanisms. Moreover, free energy perturbation calculations indicated that the insertion of catalytic water into the catalytic site is an energetically favorable process.     

Achieving specific RNA cleavage activity by an inactive splicing endonuclease subunit through engineered oligomerization

Protein-protein interaction is a common strategy exploited by enzymes to control substrate specificity and catalytic activities. RNA endonucleases, which are involved in many RNA processing and regulation processes, are prime examples of this. How the activities of RNA endonucleases are tightly controlled such that they act on specific RNA is of general interest. We demonstrate here that an inactive RNA splicing endonuclease subunit can be switched "on" solely by oligomerization. Furthermore, we show that the mode of assembly correlates with different RNA specificities. The recently identified splicing endonuclease homolog from Sulfolobus solfataricus, despite possessing all of the putatively catalytic residues, has no detectable RNA cleavage activity on its own but is active upon mixing with its structural subunit. Guided by the previously determined three-dimensional structure of the catalytic subunit, we altered its sequence such that it could potentially self-assemble thereby enabling its catalytic activity. We present the evidence for the specific RNA cleavage activity of the engineered catalytic subunit and for its formation of a functional tetramer. We also identify a higher order oligomer species that possesses distinct RNA cleavage specificity from that of previously characterized RNA splicing endonucleases.     

BPPred: a Web-based computational tool for predicting biophysical parameters of proteins

We exploit the availability of recent experimental data on a variety of proteins to develop a Web-based prediction algorithm (BPPred) to calculate several biophysical parameters commonly used to describe the folding process. These parameters include the equilibrium m-values, the length of proteins, and the changes upon unfolding in the solvent-accessible surface area, in the heat capacity, and in the radius of gyration. We also show that the knowledge of any one of these quantities allows an estimate of the others to be obtained, and describe the confidence limits with which these estimations can be made. Furthermore, we discuss how the kinetic m-values, or the Beta Tanford values, may provide an estimate of the solvent-accessible surface area and the radius of gyration of the transition state for protein folding. Taken together, these results suggest that BPPred should represent a valuable tool for interpreting experimental measurements, as well as the results of molecular dynamics simulations.     

Structure determination and characterization of carbendazim hydrochloride dihydrate

The objective of this study was to synthesize and characterize the hydrochloride salt of carbendazim with the aim of improving the intrinsic solubility of the parent compound. Carbendazim hydrochloride dihydrate was synthesized for the purpose of increasing the aqueous solubility of the parent drug, carbendazim. This was done with the commonly used saturation and cooling method. The structure was determined by single crystal radiograph crystallography, and the hydrochloride salt was found to be a dihydrate. The salt crystallized in a P 2₁ 2₁ 2₁ (#19) space group, which is typical for nonplanar, achiral, and noncentrosymmetric molecules. The asymmetric unit is comprised of 1 molecule each of carbendazim and chloride and 2 water molecules. The carbendazim molecules arrange themselves in a helical structure, with the waters and the chloride molecules in the channel linking the helix. The crystal lattice is held together by numerous hydrogen bonds, as well as van der Waals interactions. The melting point of the salt is 125.6°C. The solubility of the salt is 6.08 mg/mL, which is a thousand-fold increase from the intrinsic solubility (6.11 μg/mL) of the free base. Published: September 20, 2005     

Investigation of an Anomalously Accelerating Substitution in the Folding of a Prototypical Two-State Protein

The folding rates of two-state single-domain proteins are generally resistant to small-scale changes in amino acid sequence. For example, having surveyed here over 700 single-residue substitutions in 24 well-characterized two-state proteins, we find that the majority (55%) of these substitutions affect folding rates by less than a factor of 2, and that only 9% affect folding rates by more than a factor of 8. Among those substitutions that significantly affect folding rates, we find that accelerating substitutions are an order of magnitude less common than those that decelerate the process. One of the most extreme outliers in this data set, an arginine-to-phenylalanine substitution at position 48 (R48F) of chymotrypsin inhibitor 2 (CI2), accelerates the protein's folding rate by a factor of 36 relative to that of the wild-type protein and is the most accelerating substitution reported to date in a two-state protein. In order to better understand the origins of this anomalous behavior, we have characterized the kinetics of multiple additional substitutions at this position. We find that substitutions at position 48 in CI2 fall into two distinct classes. The first, comprising residues that ablate the charge of the wild-type arginine but retain the hydrophobicity of its alkane chain, accelerate folding by at least 10-fold. The second class, comprising all other residues, produces folding rates within a factor of two of the wild-type rate. A significant positive correlation between hydrophobicity and folding rate across all of the residues we have characterized at this position suggests that the hydrophobic methylene units of the wild-type arginine play a significant role in stabilizing the folding transition state. Likewise, studies of the pH dependence of the histidine substitution indicate a strong correlation between folding rate and charge state. Thus, mutations that ablate the arginine's positive charge while retaining the hydrophobic contacts of its methylene units tend to dramatically accelerate folding. Previous studies have suggested that arginine 48 plays an important functional role in CI2, which may explain why it is highly conserved despite the anomalously large deceleration it produces in the folding of this protein.     

Structural Determinants for Improved Stability of Designed Ankyrin Repeat Proteins with a Redesigned C-Capping Module

Designed ankyrin repeat proteins (DARPins) that specifically bind to almost any target can be obtained by ribosome display or phage display from combinatorial libraries. Although DARPins are already very stable molecules, molecular dynamics simulations, equilibrium denaturation experiments, structural studies, and recent NMR experiments suggested that the unfolding of the original C-terminal capping repeat (C-cap), taken from a natural ankyrin repeat protein, limits the stability of the initial DARPin design. Several point mutations had been introduced to optimize the C-cap and were shown to indeed further increase the stability of DARPins. We now determined crystal structures of DARPins with one or three full-consensus internal repeats (NI₁C or NI₃C) between an N-terminal capping repeat and mutants of the C-cap. An NI₁C mutant, in which the C-cap was only extended by three additional helix-forming residues, showed no structural change but reduced B-factors in the C-cap. An NI₃C C-cap mutant carrying five additional mutations in the interface to the preceding repeat, previously designed by using the consensus sequence as a guide, showed a rigid-body movement of the C-cap towards the internal repeat. This movement results in an increased buried surface area and a superior surface complementarity and explains the improved stability in equilibrium unfolding, compared to the original C-cap. A C-cap mutant with three additional mutations introducing suitably spaced charged residues did not show formation of salt bridges, explaining why its stability was not increased further. These structural studies underline the importance of repeat coupling for stability and help in the further design of this protein family.