Peptide sequence

The term amino acid sequence (including the peptide sequence, the protein sequence or primary structure of the protein) in the biochemistry of the designated sequence ( sequence) of the amino acids in a protein.

The amino acid sequence is written starting with the N-terminal amino acid. The writing direction from the N- terminus to the C -terminus corresponds to the synthesis direction of the translation on the ribosomes.

Effects on the shape of the protein

The shape of the higher structure levels ( secondary structure, tertiary structure, quaternary structure ) of the protein is apparent from the amino acid sequence. The amino acid chain of the backbone ( the backbone ) of the protein and is responsible for the covalent integrity of the inner macromolecule. During the translation, the secondary structure is a result of interactions between the amino acids. Most of these can be seen in its final form in some cases, enzymes and other environmental factors are involved in this process (see also: prion hypothesis). From the secondary structure, in turn, performance of the spatial structure ( tertiary structure ) and, if the complex with other protein subunits into complexes ( quaternary ) is shown.

At present, there is still no reliable method to predict the exact spatial arrangement of the amino acid chain on the basis of the primary structure. From experience, however, statements about existing structural elements and the function of the protein can be found in the rule.

Relationship between nucleotide sequence and amino acid sequence

The amino acid sequence of a protein can consist of the nucleotide sequence of nucleic acid in which there is coded can be derived, because the genetic code is known, each codon codes for only one amino acid. Conversely, this is not possible, since most of the amino acids have more than one codon. So you can be encoded by different nucleotide sequences. The genetic code is therefore referred to as degenerate.

The implementation of the genetic information of a gene in the amino acid sequence of a protein is a part of gene expression and protein biosynthesis. The first part of the processes is controlled by the transcription, the second is the translation.

Changes in amino acid sequence

The amino acid in the polypeptide chain may optionally be altered by post-translational modifications. Changes in the sequence of the amino acids are not, however, fragments of the ends or in the chain are cleaved. This has more or less independent subunits result. In addition, chemical changes in the amino acids are possible. It can be added to functional groups or additional bonds are formed within the molecule or with other molecules.

Analysis of the amino acid sequence

The classical method for sequencing of proteins is the Edman degradation. It was developed by Edman Pehr and consists of three steps:

1 mark the first N-terminal amino acid with phenyl isothiocyanate.

Second cleavage of the labeled amino acid.

3 the identification of the cleaved amino acid, eg by HPLC or by ion exchange chromatography.

It is followed by the repetition of the steps for the next amino acid sequencing.

The method is highly automated, and operates for peptides up to a length of about 50 amino acids. Larger proteins are cleaved prior to analysis in fragments that are sequenced separately. Lately amplified gain mass spectrometric methods in importance in this area.

Requires connected sequencing, the amino acid analysis, the quantitative determination of the protein occurring amino acids after hydrolysis.

Swell

• Protein structure
• Peptide
• Protein group