Intrinsic structural disorder and sequence features of the cell cycle inhibitor p57Kip2.

The cell cycle inhibitor p57Kip2 induces cell cycle arrest by inhibiting the activity of cyclin-dependent kinases. p57, although active as a cyclin A-CDK2 inhibitor, is largely unfolded or intrinsically disordered as shown by circular dichroism and fluorescence spectra characteristic of an unfolded protein and a hydrodynamic radius consistent with an unfolded structure. In addition, the N-terminal domain of p57 is both functionally independent as a cyclin A-CDK2 inhibitor and unstructured, as demonstrated by circular dichroism and fluorescence spectra indicative of unfolded proteins, a lack of 1H chemical shift dispersion and a hydrodynamic radius consistent with a highly unfolded structure. The amino acid compositions of full-length p57 and the excised QT domain of p57 exhibit significant deviations from the average composition of globular proteins that are consistent with the observed intrinsic disorder. However, the amino acid composition of the CDK inhibition domain of p57 does not exhibit such a striking deviation from the average values observed for proteins, implying that a general low level of hydrophobicity, rather than depletion or enrichment in specific amino acids, contributes to the intrinsic disorder of the excised p57 CDK inhibition domain.     

Complementation of buried lysine and surface polar residues in a designed heterodimeric coiled coil

The coiled coil is an attractive target for protein design. The helices of coiled coils are characterized by a heptad repeat of residues denoted a to g. Residues at positions a and d form the interhelical interface and are usually hydrophobic. An established strategy to confer structural uniqueness to two-stranded coiled coils is the use of buried polar Asn residues at position a, which imparts dimerization and conformational specificity at the expense of stability. Here we show that polar interactions involving buried position-a Lys residues that can interact favorably only with surface e' or g' Glu residues also impart structural uniqueness to a designed heterodimeric coiled coil with the nativelike properties of sigmoidal thermal and urea-induced unfolding transitions, slow hydrogen exchange and lack of ANS binding. The position-a Lys residues do not, however, confer a single preference for helix orientation, likely reflecting the ability of Lys at position a to from favorable interactions with g' or e' Glu residues in the parallel and antiparallel orientations, respectively. The Lys-Glu polar interaction is less destabilizing than the Asn-Asn a-->a' interaction, presumably reflecting a higher desolvation penalty associated with the completely buried polar position-a groups. Our results extend the range of approaches for two-stranded coiled-coil design and illustrate the role of complementing polar groups associated with buried and surface positions of proteins in protein folding and design.     

香菇的学名及其在当代真菌分类中的位置

本文综述了香菇(Lentinula edodes)的分类历史,确认其在蘑菇目(Agaricales)Tricholomataceae科下的分类地位,并证实了它与多孔菌目(Poriales)Lentinaceae科的Lentinus属没有联系。根据《真菌、地衣汉语学名命名法规》,作者讨论了译为“香菇属”的Lentinus和“小香菇属”的Lentinellus两属的汉语学名问题,提出Lentinus的汉语学名应订正为“韧伞属”,Lentinellus为“螺壳菌属”。香菇所在的Lentinula属的汉语学名建议为“木菇属”。     

CDP840

We present the in vitro characterization of a novel phosphodiesterase type 4 inhibitor, CDP840 (R-[+]-4-[2-{3-cyclopentyloxy-4-methoxyphenyl}-2-phenylethyl]pyridine), which has shown efficacy in a phase II allergen challenge study in asthmatics without adverse effects. CDP840 potently inhibits PDE-4 isoenzymes (IC₅₀ 2–30 nM) without any effect on PDE-1, 2, 3, 5, and 7 (IC₅₀>100 μM). It exhibited no significant selectivity in inhibiting human recombinant isoenzymes PDE-4A, B, C or D and was equally active against the isoenzymes lacking UCR1 (PDE-4B2 and PDE-4D2). In contrast to rolipram, CDP840 acted as a simple competitive inhibitor of all PDE-4 isoenzymes. Studies with rolipram indicated a heterogeneity within all the preparations of PDE-4 isoenzymes, indicative of rolipram inhibiting the catalytic activity of PDE-4 with both a low or high affinity. These observations were confirmed by the use of a PDE-4A variant, PDE-4A_330–886, which rolipram inhibited with low affinity (IC₅₀=1022 nM). CDP840 in contrast inhibited this PDE-4A variant with similar potency (IC₅₀=3.9 nM), which was in good agreement with theK _d of 4.8 nM obtained from [³H]-CDP840 binding studies. Both CDP840 and rolipram inhibited the high-affinity binding of [³H]-rolipram binding to PDE-4A, B, C and D with similarK _{d app} (7–19 nM and 3–5 nM, respectively). Thus, the activity of CDP840 at the [³H]-rolipram binding site was in agreement with the inhibitor’s activity at the catalytic site. However, rolipram was ∼100-fold more potent than CDP840 at inhibiting the binding of [³H]-rolipram to mouse brain in vivo. These data clearly demonstrate that CDP840 is a potent selective inhibitor of all PDE-4 isoenzymes. In contrast to rolipram, CDP840 was well-tolerated in humans. This difference, however, cannot at present be attributed to either isoenzyme selectivity or lack of activity in vitro at the high-affinity rolipram binding site (Sr).     

Phospholipid-transfer activities in cytosols from lung, isolated alveolar type II cells and alveolar type II cell-derived adenomas.

We have examined phospholipid-transfer activities in cytosols from rat and mouse whole lung, isolated rat alveolar type II cells and alveolar type II cell-derived mouse pulmonary adenomas. We report an enrichment in phosphatidylcholine and phosphatidylglycerol (but not phosphatidylinositol) protein-catalysed transfer in the type II cell and adenoma cytosols compared with the whole-lung cytosols. The activities from these cytosols were resolved using column chromatofocusing, which clearly demonstrated the presence of a phosphatidylcholine-specific transfer protein in each of the four tissues. In addition, two proteins (rat) or three proteins (mouse) catalysing both phosphatidylcholine and phosphatidylglycerol transfer were resolved from whole lung, whereas in both the rat isolated alveolar type II cells and the mouse type II cell-derived adenomas one of these less specific proteins is not present.     

Impaired formylation and uptake of tetrahydrofolate by rat small gut following cobalamin inactivation

The effect of inactivation of cobalamin by N2O on the intestinal absorption of folate was studied using rat everted gut sacs. Further, in view of uncertainties about the presence of methionine synthetase in gut [1], this enzyme was measured. Everted gut sacs were incubated with [2-14C]tetrahydrofolate, and the subsequent appearance of labelled formyl- and methyl [14C] tetrahydrofolate in everted segments of small intestine of rats was studied. Considerable methionine synthetase activity was present in washed everted gut sacs but not in gut segments in the absence of such treatment. Methionine synthetase activity declined after exposure to N2O, which oxidizes and inactivates cob(I)alamin. Folate uptake by gut sacs was not affected by 24 h exposure of the animals to N2O but fell significantly after 7 days exposure. There was a significant fall in the amount of formyltetrahydrofolate formed after cobalamin inactivation and this was reversed by supplying either methionine, methylthioadenosine or sodium formate. Serine had no effect. The data support the hypothesis that methionine and methylthioadenosine act by supplying single carbon units at the formate level of oxidation.     

A new repetitive element of the CR1 family downstream of the chicken vitellogenin gene.

We have analyzed a repetitive DNA sequence found in the 3'-flanking region of the chicken vitellogenin gene. By its sequence, the repetitive DNA has been identified as a hitherto unreported member of the chicken CR1 family of repetitive elements. The CR1 sequence displays the structural characteristics of a long terminal repeat located at the 3' end of an avian retrovirus. The CR1 element lies 2.2 kb downstream of the vitellogenin gene and 'points' away from the gene rather than toward it. In this respect, this element differs from other CR1 repeats. The CR1 element is embedded in a region showing changes in chromatin structure implying a potential role for this sequence in determining the structural state of the local chromatin.