Motifs and domains

A simple Presentation explaining the motifs HTL, HLH and a common insight about domains

1. MOTIFS AND DOMAINS By-Gouthaman PP

2. INTRODUCTION A particular arrangement of secondary structure that can be found in other proteins as well can be called a motif It is a connection of helices and sheets in different combinations Common motifs are HTH, HLH and Hairpin etc. A domain can be made up of one or more well characterised motifs which usually occur together and have independent function .

3. HTH 2 α -helices connected by a β -turn The helices are usually antiparallel Usually found in protein that bind to major and minor groves of DNA Best characterized motif for DNA binding domain One helix helps in recognition of DNA while the other stabilizes the DNA-Protein interaction Mainly involved in cell proliferation, establishment of DNA structure etc.

4. β -turn α -helices β -turn α -helices

5. HLH 2 α -helices connected by a loop The two helices tend to be of different size The larger helix aids in binding to DNA while the smaller one helps in folding and packing Associated with transcription 240 types have been identified Involved in cellular differentiation Regulation of transcription of immunoglobulins

6. Loop Long Helix Small Helix

7. DOMAINS Distinct functional units Spatially separated unit of protein Have structural and sequence resemblance to other proteins From 50-250 residues long Building blocks of molecular evolution Can be isolated by genetic engineering as they are independently stable entities Classified as α -domains, β -domains, α + β -domains and α / β -domains

8. α -domains are made of α - helices coming up and down with folds β -domains are composed of antiparallel β -sheets and generate various patterns α + β -domains are a mixture of all α and all β motifs α / β -domains are a combination of β - α - β motifs that form parallel β -sheets surrounded by antiparallel α -helices U sed by nature to generate new sequences The C and N terminals of domains are close together and allows easy slotting into parent proteins

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