The Importance of Studying Biomolecular Processes at the Single Molecular Level

Abstract

Current biomolecular studies are unevenly tilted toward using statistical methods for analyzing molecular structures. However, such a procedure may be misleading when a macromolecular assmbly is involved. Two examples will be presented in which drastically different conclusions were derived when biological processes were analyzed at single molecular level using AFM and TEM. Based on statistical methods, lipoprotein(a), a molecule highly enriched in atherosclerotic plaques, was reported to consist of one or two apolipoprotein(a) bound to one low density lipoprotein (LDL). These plaques are the leading cause of cardiovascular diseases. AFM images revealed unambiguously that one apolipoprotein(a) is bound to either one or two LDLs at one or two distant sites. This discovery led to a new theory on how lipoprotein(a) might promote LDL deposition onto the plaque. Protein self assembly to amyloid fibers is an early event in numerous human diseases, including Alzheimer's and Parkinson's diseases. Accompanying this process is a conformational change to β-sheet regardless of the protein's sequence. It was generally believed that monomers, dimers or oligomers assembled directly to the tip of a growing fiber and, for prion proteins, misfolding of the molecule led to their aggregation. AFM, and later TEM, images, however, unambiguously revealed that large spheres consisting of dozens of monomers were first formed and then assembled linearly into amyloid fibers. This discovery led to the introduction of a controversial theory, which is currently challenged by some biomedical investigators while supported by many biophysical scientists, that amyloid fiber formation is a special colloidal phenomenon, starting from colloidal particle formation and followed by their linear aggregation. Formation of the spheres, an energy minimization process, drives the protein's conformational change to β-sheet (Amyloid, 2007, 14(2):119).