AUTOMATED NOESY INTERPRETATION WITH AMBIGUOUS DISTANCE RESTRAINTS - THE REFINED NMR SOLUTION STRUCTURE OF THE PLECKSTRIN HOMOLOGY DOMAIN FROM BETA-SPECTRIN

We have used a novel, largely automated, calculation method to refine the NMR solution structure of the pleckstrin homology domain of beta-s pectrin. The method is called ARIA for Ambiguous Restraints for Iterat ive Assignment. The starting Feint for ARIA is an almost complete assi gnment of the proton chemical shifts, and a list of partially assigned NOEs, mostly sequential and secondary structure NOEs. The restraint l ist is then augmented by automatically interpreting peak lists generat ed by automated peak-picking. The central task of ARIA is the assignme nt of ambiguous NOEs during the structure calculation using a combinat ion of ambiguous distance restraints and an iterative assignment strat egy. Ln addition, ARIA calibrates ambiguous NOEs to derive distance re straints, merges overlapping data sets to remove duplicate information , and uses empirical rules to identify erroneous peaks. While the dist ance restraints for the structure calculations were exclusively extrac ted from homonuclear 2D experiments, ARIA is especially suited for the analysis of multidimensional spectra. Applied re, the pleckstrin homo logy domain, ARIA generated structures of good duality, and of suffici ently high accuracy to solve the X-ray crystal structure of the same d omain by molecular replacement. The comparison of the free NMR solutio n structure to the X-ray structure, which is complexed to D-myo-inosit ol-1,4,5-triphosphate, shows that the ligand primarily induces a disor der-order transition in the binding loops, which are disordered in the NMR ensemble but well ordered in the crystal. The structural core of the protein is unaffected, as evidenced by a backbone root-mean-square difference between the average NMR coordinates and the X-ray crystal structure for the secondary structure elements of less than 0.6 Angstr om. (C) 1997 Academic Press Limited.