ISOTOPE-EDITED INFRARED LINEAR DICHROISM - DETERMINATION OF AMIDE ORIENTATIONAL RELATIONSHIPS

A new approach for the determination of local amide orientation in ord ered insoluble proteins using linearly-polarized infrared radiation is described. The method was applied to the crystalline peptide cleromyr ine (cyclo-(GlyProLeuProGlyTyr)). Labeling of individual amide carbony l carbons with C-13 resulted in the frequency shift of the affected vi brational node, C-13 labeling allowed the amide I modes to by systemat ically assigned (''isotope editing''). Subsequently, the absorption of linearly-polarized infrared radiation was measured in order to determ ine the orientation of the individual amide carbonyl relative to the i ncident radiation (infrared linear dichroism). The relative orientatio ns of four cleromyrine amide carbonyls determined in this way were wit hin 15 degrees of those measured from the crystal structure. This meth od may be useful for the determination of amide orientation in peptide s and proteins that form oriented insoluble aggregates that are resist ant to crystallization.