[1] UNIV BASEL, BIOCTR, MAURICE E MULLER INST HIGH RESOLUT ELECTRON M, CH-4056 BASEL, SWITZERLAND
[2] MAX PLANCK INST BIOCHEM, W-8033 MARTINSRIED, GERMANY
[3] JOHNS HOPKINS UNIV, SCH MED, DEPT BIOL CHEM, BALTIMORE, MD 21205 USA
[4] JOHNS HOPKINS UNIV, SCH MED, DEPT MED, BALTIMORE, MD 21205 USA