Peptide amino terminal

Fnsion peptide (amino terminal domain of gp41)... 

Transit peptides amino-terminal extensions of precursors to chloroplast proteins which are encoded by nuclear DNA and synthesized in the cytoplasm. The T.p. are removed by Post-translational modification (see) before the protein takes on its mature configuration inside the chloroplast. The overall amino acid sequences of the T.p. are not conserved between species, but the positions of proline and the charged amino acids are highly conserved. The T.p. appear to mediate transport of the chloroplast protein precur-... 

Several enzymes, none of which are completely specific for the enkephalins, are known to cleave Leu- and Met-enkephalin at various peptide bonds. The main enzymes that degrade enkephalin are 2inc metaHopeptidases. The first enkephalin-degrading enzyme to be identified, an aminopeptidase which cleaves the amino terminal Tyr-Gly bond (179), has been shown to be aminopeptidase-N (APN) (180). It is a cytoplasmic enzyme which is uniformly distributed throughout the brain. The increased analgesic activity of synthetic enkephalins substituted by D-amino acids at position 2, eg,... 

A two-site immunometric assay of undecapeptide substance P (SP) has been developed. This assay is based on the use of two different antibodies specifically directed against the N- and C-terminal parts of the peptide (95). Affinity-purified polyclonal antibodies raised against the six amino-terminal residues of the molecule were used as capture antibodies. A monoclonal antibody directed against the carboxy terminal part of substance P (SP), covalently coupled to the enzyme acetylcholinesterase, was used as the tracer antibody. The assay is very sensitive, having a detection limit close to 3 pg/mL. The assay is fiiUy specific for SP because cross-reactivity coefficients between 0.01% were observed with other tachykinins, SP derivatives, and SP fragments. The assay can be used to measure the SP content of rat brain extracts. 

The major stmctural feature of the HAz chain (blue in Figure 5.20) is a hairpin loop of two a helices packed together. The second a helix is 50 amino acids long and reaches back 76 A toward the membrane. At the bottom of the stem there is a i sheet of five antiparallel strands. The central i strand is from HAi, and this is flanked on both sides by hairpin loops from HAz. About 20 residues at the amino terminal end of HAz are associated with the activity by which the vims penetrates the host cell membrane to initiate infection. This region, which is quite hydrophobic, is called the fusion peptide. 

Amines, Amino acids, peptides, e g tryptophan, tryptamine, peptides with terminal tryptophan groups... 

According to Charbonneau et al. (1985), aequorin is a single chain peptide consisting of 189 amino acid residues, with an unblocked amino terminal. The molecule contains three cysteine residues and three EF-hand Ca2+-binding domains. The absorption spectra of aequorin and BFP are shown in Fig. 4.1.3, together with the luminescence spectrum of aequorin and the fluorescence spectrum of BFP. 

Specific proteases located on the luminal side of the endoplasmic reticulum. They cleave the amino-terminal peptides from the precursor forms of membrane and secretory proteins. 

Fig. 24. Parallel arranged and antiparallel arranged (Pro-Ala-Gly) (n = 8,12,16). In accordance with the peptide nomenclature in which the amino terminal end, letters with mirror image were chosen in this figure (see top right). The parallel arrangement could be depicted only in this way...

Bruni, R., Taeusch, H.W., and Waring, A.J. Surfactant protein B Lipid interactions of synthetic peptides representing the amino-terminal amphipathic domain. Proc. Natl. Acad. Sci. USA 1991, 88, 7451-7455. 

Species Strain Gene/ Protein No. of amino acids including N-terminal leader peptide/N-terminal leader peptide Lattice type GenBank accession no. 

In mammals, peptide hormones typically contain only the a-amino acids of proteins finked by standard peptide bonds. Other peptides may, however, contain nonprotein amino acids, derivatives of the protein amino acids, or amino acids finked by an atypical peptide bond. For example, the amino terminal glutamate of glutathione, which participates in protein folding and in the metabolism of xenobiotics (Chapter 53), is finked to cysteine by a non-a peptide bond (Figure 3—3). The amino terminal glutamate of thyrotropin-... 

Peptides are named for the number of amino acid residues present, and as derivatives of the carboxyl terminal residue. The primary structure of a peptide is its amino acid sequence, starting from the amino-terminal residue. 

Figure 4-6. The Edman reaction. Phenylisothiocyanate derivatizes the amino-terminal residue of a peptide as a phenylthiohydantoic acid. Treatment with acid in a nonhydroxylic solvent releases a phenyithiohydantoin, which is subsequently identified by its chromatographic mobility, and a peptide one residue shorter. The process is then repeated.

The hybrid approach enhances the speed and efficiency of primary structure analysis and the range of proteins that can be sequenced. It also circumvents obstacles such as the presence of an amino-terminal blocking group or the lack of a key overlap peptide. Only a few segments of primary strucmre must be determined by Edman analysis. 

Figure 5-8. Domain structure. Protein kinases contain two domains. The upper, amino terminal domain binds the phosphoryl donor ATP (light blue). The lower, carboxyl terminal domain is shown binding a synthetic peptide substrate (dark blue).

Figure 7-7. Catalysis by chymotrypsin. The charge-relay system removes a proton from Ser 195, making it a stronger nucleophile. Activated Ser 195 attacks the peptide bond, forming a transient tetrahedral intermediate. Release of the amino terminal peptide is facilitated by donation of a proton to the newly formed amino group by His 57 of the charge-relay system, yielding an acyl-Ser 195 intermediate. His 57 and Asp 102 collaborate to activate a water molecule, which attacks the acyl-Ser 195, forming a second tetrahedral intermediate. The charge-relay system donates a proton to Ser 195, facilitating breakdown of tetrahedral intermediate to release the carboxyl terminal peptide .

Many other peptides are synthesized as proproteins that require modifications before attaining biologic activity. Many of the posttranslational modifications involve the removal of amino terminal amino acid residues by specific aminopeptidases. Collagen, an abundant protein in the extracellular spaces of higher eukaryotes, is synthesized as procollagen. Three procol-... 

There are two main classes of proteolytic digestive enzymes (proteases), with different specificities for the amino acids forming the peptide bond to be hydrolyzed. Endopeptidases hydrolyze peptide bonds between specific amino acids throughout the molecule. They are the first enzymes to act, yielding a larger number of smaller fragments, eg, pepsin in the gastric juice and trypsin, chymotrypsin, and elastase secreted into the small intestine by the pancreas. Exopeptidases catalyze the hydrolysis of peptide bonds, one at a time, fi"om the ends of polypeptides. Carboxypeptidases, secreted in the pancreatic juice, release amino acids from rhe free carboxyl terminal, and aminopeptidases, secreted by the intestinal mucosal cells, release amino acids from the amino terminal. Dipeptides, which are not substrates for exopeptidases, are hydrolyzed in the brush border of intestinal mucosal cells by dipeptidases. 

---