Structure and interfacial properties of chicken apolipoprotein A-IV.
To gain insight into the evolution and function of apolipoprotein A-IV (apoA-IV) we compared structural and interfacial properties of chicken apoA-IV, human apoA-IV, and a recombinant human apoA-IV truncation mutant lacking the carboxyl terminus. Circular dichroism thermal denaturation studies revealed that the thermodynamic stability of the alpha-helical structure in chicken apoA-IV (DeltaH = 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). Fluorescence chemical denaturation studies revealed a multiphasic red shift with a 65% increase in relative quantum yield that preceded loss of alpha-helical structure, a phenomenon previously noted for human apoA-IV. The elastic modulus of chicken apoA-IV at the air/water interface was 13.7 mN/m, versus 21.7 mN/m for human apoA-IV and 7.6 mN/m for apoA-I. The interfacial exclusion 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 that the secondary structural features of chicken apoA-IV more closely resemble those of human apoA-I, which may reflect the evolution of apoA-IV by intraexonic duplication of the apoA-I gene. However, the interfacial properties of chicken apoA-IV are intermediate between those of human apoA-I and apoA-IV, which suggests that chicken apoA-IV may represent an ancestral prototype of mammalian apoA-IV, which subsequently underwent further structural change as an evolutionary response to the requisites of mammalian lipoprotein metabolism.
Weinberg
R B
RB
Section of Gastroenterology, Department of Internal Medicine, Wake Forest University School of Medicine, Winston-Salem, NC 27157, USA.
Anderson
R A
RA
Cook
V R
VR
Emmanuel
F
F
Denefle
P
P
Hermann
M
M
Steinmetz
A
A
D000388:Air; D000818:Animals; D001054:Apolipoproteins A / Q000737:chemistry*; D002645:Chickens; D002942:Circular Dichroism; D006801:Humans; D011489:Protein Denaturation; D011994:Recombinant Proteins / Q000737:chemistry; D013499:Surface Properties; D013816:Thermodynamics; D014867:Water
D001054:Apolipoproteins A; D011994:Recombinant Proteins; C022205:apolipoprotein A-IV; D014867:Water