Assignment 2: Growth Hormone Structure

Growth hormone is a peptide hormone which is synthesized in the anterior pituitary gland. Its major structure is a single polypeptide chain, consisting of 191 amino acid residue (the number of residues vary slightly with growth hormone from different species). There are two disulfide bonds present in the growth hormone structure, located between Cys53 and Cys165. This particular structure has a molecular weight of 22, 124 daltons, or 22kD. Other isoforms of growth hormone consist of a 20kD version, and numerous dimers and polymers. The 22kD version however, accounts for approximately 70% of the growth hormone variants (Figure 1).

Figure 1: 2D Structure of Growth Hormone.

Sequence Alignment:

The sequence alignment for Cyprinus carpio (common carp), Oncorhynchus keta (chum salmon), and Carassius auratus (goldfish) was determined using Pubmed tools BLAST (basic local alignment search tool) and Clustal 2.0.8 Multiple Sequence Alignment.

BLAST locates regions of local similarity between sequences by comparing nucleotide or protein sequences to sequence databases and then calculates the statistical significance of matches. It can also be used to infer functional and evolutionary relationships between sequences. A scores table can be observed in the bottom of figure 2. This table gives numerical value to the degree of alignment between the species. Carp and Goldfish exhibited the highest score of 92, showing that they are very similar proteins. Carp and Salmon on the other hand, portrayed the lowest score of 62, showing that they are still quite similar. Goldfish and Salmon depicted a score of 67, again showing their similarity. The results from BLAST and Clustal 2.0.8 Multiple Sequence Alignment are portrayed in figure 2.

Figure 2: Alignment Results for Common Carp, Chum Salmon and Goldfish.

Key:

* Identical Residues

: Conserved Substitutions

. Semi-Conserved Substitutions

Figure 3 shows a phylogram of the alignment of the three study species. From this figure, it can be seen more clearly the relationship between the protein similarity of carp and goldfish, which are much more close than either are with salmon.

Figure 3: Phylogram Portraying the Similarity Between Three Species: Carp, Salmon and Goldfish.

References:

[1] Daughaday, W.H., Harvey, S., Scanes, C.G. (1995). Growth Hormone. Florida, USA: CRC Press.

[2] Pang, P.K.T., Scanes, C.G., Schreibman, M.P. (1993). The Endocrinology of Growth, Development, and Metabolism in Vertebrates. San Diego, California: Academic Press, Inc.

[3] Muller, E.E., Pecile, A. (1975). Growth Hormone and Related Peptides. Amsterdam: Excerpta Medica