Labelled Backbone

Figure 2. The p34 and p20-subunits of the Arp2/3-complex as heterodimer, forming the ‘backbone’ of the complex.

Figure 2. The p34 and p20-subunits of the Arp2/3-complex as heterodimer, forming the ‘backbone’ of the complex.

All subunits however are crucial for the complex; deletion of any of the subunits results in lethality (in S. cerevisiae [4]). Analysis of sub-complexes revealed that the p34 and p20 subunits together form a heterodimer critical to maintain the structural integrity of the complex; residues 1-114 and 115-236 in p34 resemble the NH2-terminal domain of p20, forming four-turn helices followed by a five-stranded antiparallel b-sheet, completed by a short helix and with an additional helix between strands 3 and 4 of the sheet. No other proteins with similar folds have been identified so far [1]. Both p43 and p20 have long COOH-terminal helices (indicated), which associate to each other with a crossing angle of around -20°; on this interface, two cavities are formed, the larger one indicated in green, the smaller one indicated in cyan. The interface is stabilized by interaction of hydrophobic residues and formation of two salt bridges.

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