The complete enzyme or holoenzyme in E. coli has a molecular weight of ,460 kD. The holoenzyme (a2bbws) can be separated into two components: the core enzyme (a2bbw) and the sigma factor (the s polypeptide), which is concerned specifically with promoter recognition.

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#Unit 1. Molecules and their Interaction Relevant to Biology

                                         Zinc Finger Motif

 


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#Unit 1. Molecules and their Interaction Relevant to Biology

                                                                  bab Motif

Two beta strands are connected by a long region containing a helix

These beta strands form parallel beta-sheets

The loop regions connecting sheet and helix can have different length

The helix axis is generally parallel to beta-sheets

Three secondary structures are stabilized by hydrophobic interactions


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#Unit 1. Molecules and their Interaction Relevant to Biology

                                             bab Motif

These motifs are generally found in right handed helix above the plane of the beta sheet

Almost all the proteins containing parallel beta sheets have this motif. 

The helix is generally not seen below the plane of beta sheets                                           

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#Unit 1. Molecules and their Interaction Relevant to Biology

                                                  bab Motif

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#Unit 1. Molecules and their Interaction Relevant to Biology

                                                           aa motif / Coiled-coils

Two helices are wound around each other

Alpha-helices are packed together through the hydrophobic interactions

These two helices are found to be stable in solution

They are generally found in transcription factors and intermediate filaments

They have heptad (7 amino acid) repeated sequences


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#Unit 1. Molecules and their Interaction Relevant to Biology

                                                        aa motif / Coiled-coils

3.6 a.a / turn in helix 

abcdefg 'a' &'d’ are hydrophobic residues 'e' and 'g' are found to be charged amino 

7.2 a.a / 2 turns acids 

 —7 amino acids per 2 turns in the helix 

For every turn there could be one hydrophobic residue coming same side of the helix 

Ex: GCN4