Plant type, amino acid sequences

The term "structural genomics" is used to describe how the primary sequence of amino acids in a protein relates to the function of that protein. Currently, the core of structural genomics is protein structure determination, primarily by X-ray crystallography, and the design of computer programs to predict protein fold structures for new proteins based on their amino acid sequences and structural principles derived from those proteins whose 3-dimensional structures have been determined. Plant natural product pathways are a unique source of information for the structural biologist in view of the almost endless catalytic diversity encountered in the various pathway enzymes, but based on a finite number of reaction types. Plants are combinatorial chemists par excellence, and understanding the principles that relate enzyme structure to function will open up unlimited possibilities for the... 

Some human proteins produced in a bacterium will not work even if the amino acid sequence is identical to the human protein. This is because our cells, and the cells of plants, animals, and yeast, add sugars to most of the proteins they produce. There are many different kinds of sugar molecules, and the type of sugar added and the place in the cell and on the protein where the sugars are added vary among cells for different species. If the correct sugars are not on the correct spot on the protein, the protein may not fit into the receptor pocket correctly, and thus not have the desired effect. Also, without the added sugars, the enzymes in our blood may destroy the protein before it can get to the appropriate spot to bind to the correct receptor. 

Table 1 lists some of the properties of the plant-type iron sulfur-proteins for which extensive study by EPR and Mossbauer spectroscopy has been reported. The physical properties summarized show that the plant-type iron sulfur proteins have molecular weights in the range from 12,000 to 24,000 and have EPR g-values (gx, gy, gz) all of the g = 1.94" type shown in Fig. 6 but with minor variations reflecting axial or nonaxial symmetry of the paramagnetic center. The amino-acid sequences of four plant-type iron-sulfur-proteins are known alfalfa (136), L. glauca (137), Scenedesmus (138), and spinach (139). Each protein has about 97 residues, all in a single peptide chain these are shown in Table 2. 

Aloe (Aloe arborescens) is a medicinal plant rich in aromatic polyketides such as pharmaceutically important aloenin (a hexaketide pyrone), aloesin (a heptaketide chromone), and barbaloin (an octaketide anthrone) (Fig. 4a). Pentaketide chromone synthase (PCS) and octaketide synthase (OKS) are novel plant-specific type III PKSs, which were obtained from the aloe plant by RT-PCR cloning using degenerate oligonucleotide primers based on the conserved sequences of known CHS enzymes [30-33]. The deduced amino acid sequences of PCS and OKS are 91% identical (368/403), and show 50-60% identity to those of other CHS superfamily type III PKSs of plant origin OKS shares 60% identity (240/403) with CHS from... 

Up to four cDNA clones have been isolated for potato BE - one for 91 to 99 kDa.253-255 All these allelic clones have sequences similar to those of the BEI type. Also, the sbelc allele codes for a mature enzyme of 830 amino acids with a MW of 95.18 kDa. The sbelc BE protein product, expressed in E. coli, migrates as a 103 kDa protein.253 It is of interest to note that BE isolated from other plants, bacteria and mammals have molecular masses ranging from 75 to —85 kDa. These molecular weights are consistent with the molecular weights obtained from deduced amino acid sequences obtained from isolated genes or cDNA clones. 

Chloroplast type of CuZn-SOD isozyme is localized in the chloroplast stroma of most plants, whereas Fe-SOD occurs in chloroplasts of Euglena, the moss Marchantia polymorpha and several species of seed plant. So far Mn-SOD has not been detected in chloroplasts in a soluble form but occurs in a thylakoid membrane-bound form.23,24) The cytosolic CuZn-SOD, which is distinguishable from the chloroplastic CuZn-SOD in terms of amino acid sequence, occurs in cell compartments other than chloroplasts and in nonphotosynthetic tissues.14)... 

BPS catalyzed the stepwise condensation of benzoyl-CoA with three molecules of malonyl-CoA to give a tetraketide intermediate that was cyclized by intramolecular Claisen condensation into 2,4,6-trihydroxybenzophenone (Figure 2). The enzyme was inactive with CoA-linked ciimamic acids such as 4-coumaroyl-CoA, the preferred starter substrate for chalcone synthase (CHS). BPS and CHS from H. androsaemum cell cultures shared 60.1% amino acid sequence identity. CHS is ubiquitous in higher plants and the prototype enzyme of the type III PKS superfamily (1,2). It uses the same reaction mechanism like BPS to form 2, 4,4, 6 -tetrahydroxychalcone, the precursor of flavonoids (Figure 2). 

The outgroup was the consensus sequence of four bacterial type 111 PKSs. The bacterial enzymes extend the array of the polyketide scaffolds. They share only -25% amino acid sequence identity with plant PKSs and each other 43). The phylogenetic tree reflected the systematic grouping of the higher plants. The PKSs from angiosperms fall into two clusters. One cluster comprises CHSs including the enzymes from H. androsaemum and S. aucuparia cell cultures. 

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