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	Amino Acid Sequences of Proteins- The amino acids were conventionally represented by three letter symbols, e.g., Ala for alanine, Val for valine, etc. But in bioinformatics, they are denoted by single letters, e.g., A for alanine, C for cystine, D for aspartic acid, etc. But some positions in protein sequences have ambiguities; this situation is comparable to that for DNA sequences.
For example, it may not be clear that a position has glutamine or glutamic acid; such a position is given the symbol Glx. Similarly, Asx denotes either asparagine or aspartic acid. The symbol X is used to denote that the position may have any amino acid. The protein synthesis begins at the N-terminus and proceeds to the C-terminus. The amino acid sequences in databases are listed from the N-terminus (at the extreme left of the sequence) to the C-terminus (at the extreme right) of the polypeptide.