Structure and Antigenicity of Hen Egg‐White Lysozyme Fragments

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Abstract
Under controlled conditions of pepsin digestion of hen egg‐white lysozyme, large fragments with composition identical to sequence 57—107 and sequence (57—83) + (91—107), have been obtained.Inhibition of lysozyme‐anti‐lysozyme precipitation by these fragments, showed that section 84—90 is important for the antigenic specificity of fragment 57—107. The position of one lysozyme antigenic region was suggested, namely section 85—90 combined with a region close to methionine 105, reacting with about 10% of total anti‐lysozyme antibodies. Structure evaluation of the purified peptides through circular dichroism, revealed that only 30% of the “native” alpha‐helicity amount (ie. the amount of helicity this fragment possesses when integrated in the lysozyme molecule) remained. We concluded that in the case of lysozyme, mainly long‐range interactions stabilize the native configuration. Secondly, that differences in antigenic specificity among related peptides are not due to differences in structure. Fragment‐antibody interaction could be explained by assuming the existence of a simple equilibrium Fr⇌ Fn between the completely random and the native fragment, or, through an “induced fint” mechaism.