Structural Features of Azurin at 2.7 Å Resolution

Abstract

The phases for the x‐ray data for crystals of azurin from P. aeruginosa have been refined and extended from 3 Å to 2.7 Å resolution by a method based on the direct space averaging of the electron density of the four molecules in the asymmetric unit. The electron density in the present map is much improved over the earlier one, and most of the side‐chains are now evident. In the detailed fitting of a model to the present map, an alternative interpretation, conforming to the plastocyanin model and reversing the chain directions in strands one and two of the original azurin model, was found to better represent certain features of the present map. The surface of the molecule closest to the copper consists of an extended region of invariant or semiconserved hydrophobic residues. There is not a region of conserved charge that is not paired with a compensating charge.

Structural models of the redox centres in cytochrome oxidase.

“…The three-dimensional structure of Pseudomonas azurin (Adman and Jensen, 1981) was taken from the Brookhaven Protein Data Bank.…”

A New Type 2 Copper Cysteinate Azurin

“…Type 1 copper sites are characterized by an intense absorption band near 600 nm (⑀ ϭ 3,000 -6,000 M Ϫ1 cm Ϫ1 ) and by EPR spectra with unusually small A values (A Ͻ 70 ϫ 10 Ϫ4 cm Ϫ1 ) (1). The copper ion in azurin is coordinated by three strong ligands (S ␥ of Cys 112 and N ␦ of His 117 and His 46 ) forming a trigonal plane around the copper and two weak axial ligands (S ␦ of Met 121 and backbone oxygen of Gly 45 ) (2,3). Much has been learned about coordination geometry in cupredoxins by removal and replacement of copper ligands.…”

Long-range intramolecular electron transfer in azurins.

“…All azurins sequenced to date have an intrachain disulfide bridge connecting residues Cys-3 to Cys-26 (13). In the three-dimensional fold, this disulfide is at the bottom of the (3-barrel structured protein, some 2.0 nm away from the copper site (14)(15)(16). We have earlier observed that this disulfide bridge can be reduced to form the RSSRradical ion (17 The publication costs of this article were defrayed in part by page charge payment.…”

“…Since in P. aeruginosa azurin the indole ring ofTrp-48 is aligned along an axis connecting the disulfide bond with the copper center (Fig. 6), we do use the above value for P. Inserting 8 = 12 nm-1 and an edge to edge distance, r -ro = 2.0 nm from the RSSR-to the copper site in P. aeruginosa azurin (14)(15)(16), we calculate AS* (P. aeruginosa azurin) = 143 J K-l mol-1. This yields for AG* = AIH*-TAS* = 4.9 kJ-mol-1.…”