Surface-Core Relationships in Human Low Density Lipoprotein as Studied by Infrared Spectroscopy

Abstract

The secondary structure of human apolipoprotein B at 37 degrees C is estimated to be 24% alpha-helix, 23% beta-sheet, 6% beta-turns, 24% unordered structure, and 24% "beta-strands," characterized by a band around 1618 cm-1, and consistent with extended string-like chains in contact with the lipid moiety not forming beta-sheets. When cooled to a temperature below the cholesteryl ester transition at 30 degrees C, the ordering of the low density lipoprotein core results in reversible changes in the protein conformation, decreasing the apparent amount of alpha-helix, beta-strand, and unordered structure below 30 degrees C and increasing beta-sheet and beta-turns. Lowering the ionic strength affects the core-associated transitions, shifting their temperature from 30 to 20 degrees C, and modifying protein conformation below the transition. An additional thermal event is observed at 75 degrees C, leading to irreversible protein denaturation. In the broad temperature range between the 30 and 75 degrees C transitions, apolipoprotein B is stable toward both temperature and ionic strength changes. After thermal denaturation, the protein retains a certain degree of ordered structure.

Infrared evidence of a β‐hairpin peptide structure in solution

“…The [3-hairpin bands corresponding to the extended structure are seen to differ in two aspects from ordinary antiparallel 13-sheets; first, the low frequency bands appear around 1620 cm -1 and second, in the high frequency component the expected isotopic shift is not produced. Both characteristic features have also been found in concanavalin A [9] and in apoB-100 from LDL [10], where bands from extended structure located below 1630 cm -1 have been dis-S0014-5793/96/$12.00 © 1996 Federation of European Biochemical Societies. All rights reserved.…”

Infrared studies of protein-induced perturbation of lipids in lipoproteins and membranes

“…Also the structure of the lipid-attached protein has been described by IR in combination with proteolytic digestion (Goormaghtigh et al, 1993). Bañ uelos et al (1995) have investigated conformational changes induced in apo B by changes in temperature and in ionic strength, and taken advantage of the IR ability to record data on lipid and protein moieties simultaneously. This allows the direct study of surface-core relationships in the lipoprotein.…”

Mechanism of thermal denaturation of maltodextrin phosphorylase from Escherichia coli

“…In particular, the 1653n8 cm −" band is due to α-helical structure while β-sheets display a band at 1638 and 1639 cm −" . The 1693n7 and the 1685n4 cm −" bands can also be assigned to β-structure [32] while the bands at 1679n9 and 1671n7 cm −" are probably due to turns [32]. The other bands displayed in Figure 3A may be assigned to amino acid side chain absorption [32,33].…”

“…The 1693n7 and the 1685n4 cm −" bands can also be assigned to β-structure [32] while the bands at 1679n9 and 1671n7 cm −" are probably due to turns [32]. The other bands displayed in Figure 3A may be assigned to amino acid side chain absorption [32,33]. Figure 3B shows that the secondary structure of precipitated MalP is quite different compared with that of the soluble part of the enzyme.…”