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Methionine sulphoxide reductases (Msr) catalyse the reduction of oxidized methionine to methionine. These enzymes are divided into two classes, MsrA and MsrB, according to substrate specificity. Although most MsrA and MsrB exist as separate enzymes, in some bacteria these two enzymes are fused to form a single polypeptide (MsrAB). Here, we report the first crystal structure of MsrAB from Streptococcus pneumoniae (SpMsrAB) at 2.4 Å resolution. SpMsrAB consists of an N-terminal MsrA domain, a C-terminal MsrB domain and a linker. The linker is composed of 13 residues and contains one 310-helix and several hydrogen bonds interacting with both MsrA and MsrB domains. Interestingly, our structure includes the MsrB domain complexed with an SHMAEI hexa-peptide that is the N-terminal region of neighbouring MsrA domain. A kinetic analysis showed that the apparent Km of SpMsrAB for the R-form-substrate was 20-fold lower than that for the S-form substrate, indicating that the MsrB domain had a much higher affinity for the substrate than the MsrA domain. Our study reveals the first structure of the MsrAB by providing insights into the formation of a disulphide bridge in the MsrB, the structure of the linker region, and the distinct structural nature of active site of each MsrA and MsrB domain.

Characteristic growth patterns of Cordyceps militaris isolates on various media, under varying light conditions and at varying incubation periods were examined. Light was found to be the most critical single factor in determining the density, texture, and pigmentation of the mycelial culture of the fungus. However, under the light condition, the degree of pigmentation and mycelial density were found to be affected by the incubation period and type of medium. Irrespective of the variations in medium type or incubation period, there was no pigmentation of the mycelium under dark condition. Radial growth of the mycelium was faster under dark incubation rather than under light incubation. Abundant mycelial density and darkest pigmentation of C. militaris isolates were produced in nutritionally rich media like SDAY, SMAY and CZYA, suggesting that these media may fulfill all the requirements for vegetative growth of the fungus. Growth characteristics of C. militaris isolates could be easily observed by the simple agar culture method, which would be useful to characterize the phenotypic characteristics of large number of pure cultures of the fungus under given conditions of growth factors such as medium, light and temperature.

The two-photon absorption (TPA) cross section and the second hyperpolarizability (γ) of the linear quadrupolar molecule are theoretically investigated by using the ab initio calculation methods for a few series of quadrupolar molecules. The relationships between the molecular structure and the TPA as well as the NLO property are established. It is found that, as the strengths of donors and acceptors increase, (i) both the energy gap between the first excited electronic state, |e>, and the ground electronic state, |g>, and that between the TPA-allowed excited electronic state |f> and |g> decrease, (ii) the energy gap difference, |E fe − E eg |, which is the detuning factor affecting the TPA matrix element, decreases, and (iii) the product of the transition dipole matrix elements, | |, associated with the TPA increases. These effects are combined to make the TPA cross section monotonically increase as the donor and acceptor strengths increase. The second hyperpolarizabilities of the same series of quadrupolar molecules are also calculated by using both the finite-field method and sum-over-state method. The relationship between the TPA and second hyperpolarizability is briefly discussed.

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The DNA topoisomerase inhibitor beta-lapachone is a quinone obtained from the bark of the lapacho tree (Tabebuia avellanedae) in South America. It has been reported to possess a wide range of pharmacological properties, and is a promising cancer chemopreventive agent. In this study, the effects of beta-lapachone on the growth of the human hepatoma cell line HepG2 were investigated. The results showed that beta-lapachone inhibits the viability of HepG2 by inducing apoptosis, as evidenced by the formation of apoptotic bodies and DNA fragmentation. Reverse transcription-polymerase chain reaction and immunoblotting results indicated that treatments of cells with beta-lapachone resulted in down-regulation of anti-apoptotic Bcl-2 and Bcl-X(L) and up-regulation of pro-apoptotic Bax expression. beta-Lapachone-induced apoptosis was associated with a proteolytic activation of caspase-3 and -9 and degradation of poly(ADP-ribose) polymerase protein. However, beta-lapachone treatment did not affect the inhibitor of apoptosis proteins family and the Fas/FasL system. Taken together, our study indicated that beta-lapachone may have potential as a chemopreventive agent for liver cancer.

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