北京棒杆菌天冬氨酸激酶突变体A380H的酶学性质

同源序列比对和蛋白质结构分析表明,A380为天冬氨酸激酶(aspartate kinase,AK)的绝对保守位点,对该位点进行定点突变、分离纯化和性质表征.结果表明:与野生型(WT)相比,突变体A380H的V_(max)提高4.28倍;突变体A380H的最适温度由28℃提高至35℃,最适pH值仍为7.5,半衰期由4.5h缩短至3.5h;底物抑制剂对WT和突变体均有抑制作用,苏氨酸和赖氨酸呈协同抑制作用,苏氨酸单独存在时对A380H具有激活或抑制减弱作用;Mg~(2+),Ni ~(2+)对WT有激活作用,1,5mmol/L的Cu~(2+)对A380H有激活作用;与WT相比,甲醇和异丙醇对A380H的抑制作用增强,正丁醇和乙腈对A380H的抑制作用减弱且表现出激活作用.     

蛋白质组学的研究方法

综述了近年来蛋白质组学研究中较为重要的蛋白质分离、蛋白质鉴定、蛋白质相互作用以及生物信息学等技术.     

水稻蛋白质激酶CK2催化亚基的表达和活性测定

用RT-PCR的方法分离到了水稻蛋白质激酶CK2催化亚基（OsCK2α）的cDNA,通过大肠杆菌高效表达系统表达了OsCK2α,并利用亲合层析的方法纯化了重组蛋白质GST—OsCK2α．得到的大肠杆菌重组蛋白质GST—OsCK2α能够体外磷酸化CK2的常用底物酪蛋白,并且该磷酸化反应能够被CK2的特异性抑制剂肝素所抑制,研究表明重组CK2α具有典型的蛋白质激酶CK2的活性,为研究水稻CK2及其底物的功能奠定了基础．     

河南小麦籽粒中粗蛋白质和赖氨酸含量的初步研究

通过三年来对河南省578份小麦品种样品的分析结果:河南省小麦籽粒粗蛋白质(干基)含量多数在13.12～16.32％之间,平均为14.72％;赖氨酸(干基)含量多数在0.34～0.46％之间,平均为0.401％,在全国各省市中居中上等水平。发现河南小麦籽粒中粗蛋白质和赖氨酸含量有较大的不稳定性。在生产实践中对优质育种和科学栽培二者不可偏废。     

The DnaK/ClpB chaperone system from <Emphasis Type="Italic">Thermus thermophilus</Emphasis>

Proteins of thermophilic organisms are adapted to remain well structured and functional at elevated temperatures. Nevertheless like their 'cousins' that reside at medium temperatures, they require the assistance of molecular chaperones to fold properly and prevent aggregation. This review compares structural and functional properties of the DnaK/ClpB systems of Thermus thermophilus and, mainly, Escherichia coli (Dnak_Tth and Dnak_Eco). Many elemental properties of these systems remain conserved. However, in addition to a general increase of the thermal stability of its components, the Dnak_Tth system shows profound differences in its regulation, and genetic as well as oligomeric organization. Whether these differences are unique or represent general strategies of adaptation to life at elevated temperatures remains to be clarified. RID="*" ID="*"Corresponding author.     

Novel regulation and function of Src tyrosine kinase

Src tyrosine kinase is a critical signal transducer that modulates a wide variety of cellular functions. Misregulation of Src leads to cell transformation and cancer. Heterotrimeric guanine-nucleotide-binding proteins (G proteins) are another group of signaling molecules that transduce signals from cell-surface receptors to generate physiological responses. Recently, it was discovered that Gαs and Gαi could directly stimulate Src family tyrosine kinase activity. This novel regulation of Src tyrosine kinase by G proteins provides insights into the adenylyl cyclase-independent signaling mechanisms involved in ligand-induced receptor desensitization, internalization and other physiological processes. Received 17 August 2001; received after revision 22 October 2001; accepted 24 October 2001     

Specific localization of the catalytic subunits of protein kinase CK2 at the centrosomes

The protein kinase CK2 holoenzyme is composed of two regulatory β subunits and two catalytic α or α' subunits. Although experimental evidence for involvement of the enzyme in the regulation of cell proliferation is accumulating, the exact mechanism of its action is still unclear. The subcellular localization of the enzyme may be a key to its function. We have recently shown that the CK2 holoenzyme is tightly associated with the Golgi complex and the endoplasmic reticulum. Centrosomes, which organize spindle formation during the cell cycle and microtubule cytoskeleton formation and, thereby, the location and orientation of different organelles in the cell, are in close vicinity to the Golgi complex. Because several kinases and phosphatases have been described to regulate the functions of the centrosome, we analysed the association of CK2 with these organelles. Using biochemical cell fractionation and coimmunoprecipitation, we never found the holoenzyme but only the catalytic asubunits associated with the centrosome. These data were confirmed by immunoelectron microscopy. Thus, the present data point to a particular role of the catalytic α and α' subunit of protein kinase CK2, which may be different from their roles in the holoenzyme. Received 2 August 2002; received after revision 2 October 2002; accepted 22 October 2002 RID="*" ID="*"Corresponding author.     

Distribution of tightened end fragments of globular proteins statistically matches that of topohydrophobic positions: towards an efficient punctuation of protein folding?

Using a set of 372 proteins representative of a variety of 56 distinct globular folds, a statistical correlation was observed between two recently revealed features of protein structures: tightened end fragments or 'closed loops', i. e. sequence fragments that are able in three-dimensional (3D) space to nearly close their ends (a current parameter of polymer physics), and 'topohydrophobic positions', i. e. positions always occupied in 3D space by strong hydrophobic amino acids for all members of a fold family. Indeed, in sequence space, the distribution of preferred lengths for tightened end fragments and that for topohydrophobic separation match. In addition to this statistically significant similarity, the extremities of these 'closed loops' may be preferentially occupied by topohydrophobic positions, as observed on a random sample of various folds. This observation may be of special interest for sequence comparison of distantly related proteins. It is also important for the ab initio prediction of protein folds, considering the remarkable topological properties of topohydrophobic positions and their paramount importance within folding nuclei. Consequently, topohydrophobic positions locking the 'closed loops' belong to the deep cores of protein domains and might have a key role in the folding process. Received 1 February 2001; accepted 7 February 2001     

玉米渣多微发酵生产蛋白饲料的研究

采用固态多微混合发酵方式，进行以玉米淀粉渣为原料生产蛋白饲料的研究。通过从自然界分离的多株菌种进行诱变，筛选出能够很好降解玉米渣中纤维素物质的黑曲霉菌株Ｈ１和酵母菌Ａ、Ｂ。经研究发现，Ｈ１和Ａ、Ｂ酵母菌混合培养后，培养物中粗蛋白含量达２１．９％，纤维素转化率为４３．２１％，氨基酸组成齐全，并富含多各酶类。