Amino acid sequences and

Fig. 1. Primary stmcture of hGH showing the amino acid sequence and the disulfide bonds.

Enzymes are excellent catalysts for two reasons great specificity and high turnover rates. With but few exceptions, all reac tions in biological systems are catalyzed by enzymes, and each enzyme usually catalyzes only one reaction. For most of the important enzymes and other proteins, the amino-acid sequences and three-dimensional structures have been determined. When the molecular struc ture of an enzyme is known, a precise molecular weight could be used to state concentration in molar units. However, the amount is usually expressed in terms of catalytic activity because some of the enzyme may be denatured or otherwise inactive. An international unit (lU) of an enzyme is defined as the amount capable of producing one micromole of its reaction product in one minute under its optimal (or some defined) reaction conditions. Specific activity, the activity per unit mass, is an index of enzyme purity. 

The eight-stranded a/p-barrel stmcture is one of the largest and most regular of all domain stmctures. A minimum of about 200 residues are required to form this structure. It has been found in many different proteins, most of which are enzymes, with completely different amino acid sequences and... 

Figure 4.10 Consensus amino acid sequence and secondary structure of the leucine-rich motifs of type A and type B. "X" denotes any...

The a/p-barrel structure is one of the largest and most regular of all domain structures, comprising about 250 amino acids. It has so far been found in more than 20 different proteins, with completely different amino acid sequences and different functions. They are all enzymes that are modeled on this common scaffold of eight parallel p strands surrounded by eight a helices. They all have their active sites in very similar positions, at the bottom of a funnel-shaped pocket created by the loops that connect the carboxy end of the p strands with the amino end of the a helices. The specific enzymatic activity is, in each case, determined by the lengths and amino acid sequences of these loop regions which do not contribute to the stability of the fold. 

Most of the known antiparallel p structures, including the immunoglobulins and a number of different enzymes, have barrels that comprise at least one Greek key motif. An example is 7 crystallin, which has two consecutive Greek key motifs in each of two barrel domains. These four motifs are homologous in terms of both their three-dimensional structure and amino acid sequence and are thus evolutionarily related. 

Fibrous proteins are long-chain polymers that are used as structural materials. Most contain specific repetitive amino acid sequences and fall into one of three groups coiled-coil a helices as in keratin and myosin triple helices as in collagen and p sheets as in silk and amyloid fibrils. 

The coiled-coil fibrous proteins have heptad repeats in their amino acid sequence and form oligomers—usually dimers or trimers—through their coiled coils. These oligomeric units then assemble into fibers. 

The ultimate goal of protein engineering is to design an amino acid sequence that will fold into a protein with a predetermined structure and function. Paradoxically, this goal may be easier to achieve than its inverse, the solution of the folding problem. It seems to be simpler to start with a three-dimensional structure and find one of the numerous amino acid sequences that will fold into that structure than to start from an amino acid sequence and predict its three-dimensional structure. We will illustrate this by the design of a stable zinc finger domain that does not require stabilization by zinc. 

Proteins have unique amino acid sequences, and it is this uniqueness of sequence that ultimately gives each protein its own particular personality. Because the number of possible amino acid sequences in a protein is astronomically large, the probability that two proteins will, by chance, have similar amino acid sequences is negligible. Consequently, sequence similarities between proteins imply evolutionary relatedness. 

C. B. Anfinsen (Bethesda) work on ribo-nuclease, especially concerning the connection between the amino-acid sequence and the biologically active conformation. 

A constellation of genes code for PBPs of varying amino acid sequences and functionalities. PBPs occur as free-standing polypeptides and as protein fusions. This combinatorial system of structural modules results in a large increase in diversity. 

The structure of all TK receptors is similar in terms of expression oiTACR genes, since all these genes contain five exons intercalated by four introns [1, 5]. Exon I encodes for the N-terminal extracellular tail, the first intracellular (IC1) and extracellular (EC1) loops and the first, second, and third transmembrane domains (TM1, TM2, and TM3). Exon II encodes for the second intracellular (IC2) and extracellular (EC2) loops and the fourth transmembrane domain (TM4). Exon III encodes for the fifth transmembrane domain (TM5) and the third intracellular loop (IC3). Exon IV encodes for the sixth and seventh transmembrane domains (TM6 and TM7) and the third extracellular loop. Exon V encodes for the C-terminal intracellular tail only. A schematic drawing of the amino acid sequences and TK receptor organization is shown in Fig. 1. 

Structural information chemical formula and stereochemistry in the case of a New Chemical Entity (NCE) or amino acid sequence and glycosylation sites in the case of a biotech product... 

The presence of three polypeptides in Table 5.8 tliat were not predicted from the relationship between the amino acid sequence and the enzyme used for digestion is worthy of note when interpretation of data of this sort is undertaken. The MALDI data showed six further unexpected polypeptides, none of which were detected in the LC-MS data ... 

Consensus sequences similar to ori or ARS in structure or function have not been precisely defined in mammalian cells, though several of the proteins that participate in ori recognition and function have been identified and appear quite similar to their yeast counterparts in both amino acid sequence and function. 

The goals of the project were to confirm the molecular weight of hementin, determine the N-terminal amino acid sequence, and provide sufficient purified protein for biochemical studies of the fibrinolytic activity. These goals were all attained. Many of the issues that become important in devising a scalable process were identified, particularly... 

T10. Tani, K Fujii, H.,Nagata, S and Miwa, S Human liver type pyruvate kinase Complete amino acid sequence and the expression in mammalian cells. Proc. Natl. Acad. Sci. U.S.A. 85, 1792-1795 (1988). 

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