Structure and interfacial properties of chicken apolipoprotein A-IV

To gain insight into the evolution and function of apolipoprotein A-IV (apo A-IV) we compared structural and interfacial properties of chicken apoA-IV human apoA-IV, and a recombinant human apoA-IV truncation mutant lacking th e carboxyl terminus, Circular dichroism thermal denaturation studies reveal ed that the thermodynamic stability of the alpha-helical structure iu chick en apoA-IV (Delta H = 71.0 kcal/mol) was greater than that of human apoA-IV (63.6 kcal/mol) but similar to that of human apoA-I (73.1 kcal/ mol). Fluo rescence chemical denaturation studies revealed a multiphasic red shift wit h a 65% increase in relative quantum yield that preceded loss of alpha-heli cal structure, a phenomenon previously noted for human apoA-IV. The elastic modulus of chicken apoA-IV at the air/water interface tvas 13.7 mN/m, vers us 21.7 mN/m for human apoA-IV and 7.6 mN/m For apoA-I. The interfacial exc lusion pressure of chicken apoA-IV for phospholipid monolayers was 31.1 mN/ m, versus 33.0 mN/m for human A-I and 28.5 mN/m for apoA-IV. We conclude th at the secondary structural features of chicken apoA-IV more closely resemb le those of human apoA-I, which may reflect the evolution of apoA-IV by int raexonic duplication of the apoA-I gene. However, the interfacial propertie s of chicken apoA-IV are intermediate between those of human apoA-I and apo A-IV, which suggests that chicken apoA-IV may represent an ancestral protot ype of mammalian apoA-IV, which subsequently underwent further structural c hange as an evolutionary response to the requisites of mammalian lipoprotei n metabolism.-Weinberg, R. B., R. A. Anderson, V. R. Cook, Emmanuel, P. Den efle, M. Hermann, and A. Steinmetz. Structure and interfacial properties of chicken apolipoprotein A-IV.