Biomedical subjects

Shang-Rong Ji

Publications and source records attributed to Shang-Rong Ji.

6 recordsLinked to original sources

PubMed2006

Cell membranes and liposomes dissociate C-reactive protein (CRP) to form a new, biologically active structural intermediate: mCRP(m).

Emerging evidence indicates that C-reactive protein (CRP) has at least two conformationally distinct isoforms, i.e., pentameric CRP (pCRP) and monomeric CRP (mCRP or CRP subunit). Both CRP isoforms are proposed to play roles in inflammation and may participate in the pathogenesis of cardiovascular disease. However, the origin of mCRP in situ and the interplay between the two CRP isoforms under physiological/pathological circumstances remain elusive. Herein, by probing conformational alteration, neoepitope expression, and direct visualization using electron-microscopy, we have shown that calcium-dependent binding of pCRP to membranes, including liposomes and cell membranes, led to a rapid but partial structural change, producing molecules that express CRP subunit antigenicity but with retained native pentameric conformation. This hybrid molecule is herein termed mCRP(m). The formation of mCRP(m) was associated with significantly enhanced complement fixation. mCRP(m) can further detach from membrane to form the well-recognized mCRP isoform converted in solution (mCRP(s)) and exert potent stimulatory effects on endothelial cells. The membrane-induced pCRP dissociation not only provides a physiologically relevant scenario for mCRP formation but may represent an important mechanism for regulating CRP function.

Animals↗

PubMed2006

Effect of modified C-reactive protein on complement activation: a possible complement regulatory role of modified or monomeric C-reactive protein in atherosclerotic lesions.

OBJECTIVE: The capacity of human C-reactive protein (CRP) to activate/regulate complement may be an important characteristic that links CRP and inflammation with atherosclerosis. Recent advances suggest that in addition to classical pentameric CRP, a conformationally distinct isoform of CRP, termed modified or monomeric CRP (mCRP), may also play an active role in atherosclerosis. Although the complement activation behavior of CRP has been well established, the capacity of mCRP to interact with and activate the complement cascade is unknown. METHODS AND RESULTS: mCRP bound avidly to purified C1q, and this binding occurred primarily through collagen-like region of C1q. Fluid phase mCRP inhibited the activation of complement cascade via engaging C1q from binding with other complement activators. In contrast, when immobilized or bound to oxidized or enzymatically modified low-density lipoprotein, mCRP could activate classical complement pathway. Low-level generation of sC5b-9 indicated that the activation largely bypassed the terminal sequence of complement, which appears to involve recruitment of Factor H. CONCLUSIONS: These results indicate that mCRP can both inhibit and activate the classical complement pathway by binding C1q, depending on whether it is in fluid phase or surface-bound state.

Atherosclerosis↗

PubMed2005

Interactions of C-reactive protein with low-density lipoproteins: implications for an active role of modified C-reactive protein in atherosclerosis.

The interaction of C-reactive protein with low-density lipoprotein is considered to be one of the key properties that link C-reactive protein with atherosclerosis. However the data obtained to date are controversial, and hence make it difficult to conclude actual physiological or pathological impact of such interaction. The incompatible findings could be ascribed to the different structural state of C-reactive protein and/or low-density lipoprotein. We investigated in detail the interaction of various C-reactive protein isoforms with native and modified low-density lipoprotein. Our data showed "C-reactive protein" could indeed interact with each of native low-density lipoprotein, oxidized or enzymatically modified low-density lipoprotein, but that interaction occurs primarily when C-reactive protein is conformed in a modified form and not pentameric structure. Low level of modified C-reactive protein "contaminant" could confer C-reactive protein obvious low-density lipoprotein binding capacity. Interaction of modified C-reactive protein and low-density lipoprotein was mediated synergistically by both electrostatic association with ApoB and hydrophobic insertion into lipid layer. When complexed with modified C-reactive protein, macrophage binding/uptake of native and oxidized low-density lipoprotein was either increased 150% or decreased 35%, respectively. Thus the interaction of modified C-reactive protein with low-density lipoprotein may contribute to the regulation of low-density lipoprotein metabolism and foam cell formation in arterial wall. These results highlight an active role of modified C-reactive protein in atherosclerotic process.

Atherosclerosis↗

PubMed2003

Two-dimensional crystallization of rabbit C-reactive protein monomeric subunits.

C-reactive protein (CRP) is one of the most characteristic acute-phase proteins. Modified CRP is the monomeric form of native CRP and has recently been suggested to exist under physiological conditions. In the current work, CRP subunits were separated from stock CRP solution by size-exclusion chromatography. Two forms of two-dimensional crystals composed of monomeric CRP were obtained on negatively charged lipid monolayers: a previously reported form, MI, and a new form, MII. A projection map at 2.0 nm resolution of the two-dimensional MII crystals was obtained. The formation of the two forms of two-dimensional crystal exhibited a dependence on pH. At pH values of less than 5.5 the subunits assembled in MI packing, while at pH values greater than 6.5 they assembled in MII packing. When using modified CRP prepared by acidic denaturation, only MI crystals could be formed. The fact that CRP subunits produced by dissociation or denaturation could form highly ordered two-dimensional crystals indicates that they have a certain homogeneous structure, which supports the previous suggestion of the existence of modified CRP in vivo.

Animals↗

PubMed2003

Visualization of synaptotagmin I oligomers assembled onto lipid monolayers.

Neuronal exocytosis is mediated by Ca(2+)-triggered rearrangements between proteins and lipids that result in the opening and dilation of fusion pores. Synaptotagmin I (syt I) is a Ca(2+)-sensing protein proposed to regulate fusion pore dynamics via Ca(2+)-promoted binding of its cytoplasmic domain (C2A-C2B) to effector molecules, including anionic phospholipids and other copies of syt. Functional studies indicate that Ca(2+)-triggered oligomerization of syt is a critical step in excitation-secretion coupling; however, this activity has recently been called into question. Here, we show that Ca(2+) does not drive the oligomerization of C2A-C2B in solution. However, analysis of Ca(2+).C2A-C2B bound to lipid monolayers, using electron microscopy, revealed the formation of ring-like heptameric oligomers that are approximately 11 nm long and approximately 11 nm in diameter. In some cases, C2A-C2B also assembled into long filaments. Oligomerization, but not membrane binding, was disrupted by neutralization of two lysine residues (K326,327) within the C2B domain of syt. These data indicate that Ca(2+) first drives C2A-C2B.membrane interactions, resulting in conformational changes that trigger a subsequent C2B-mediated oligomerization step. Ca(2+)-mediated rearrangements between syt subunits may regulate the opening or dilation kinetics of fusion pores or may play a role in endocytosis after fusion.

Animals↗

PubMed2001

Cholesterol is an important factor affecting the membrane insertion of beta-amyloid peptide (A beta 1-40), which may potentially inhibit the fibril formation.

beta-Amyloid peptide (A beta), a normal constituent of neuronal and non-neuronal cells, has been proven to be the major component of extracellular plaque of Alzheimer's disease. Interactions between A beta and neuronal membranes have been postulated to play an important role in the neuropathology of Alzheimer's disease. Here we show that A beta is able to insert into lipid bilayer. The membrane insertion ability of A beta is critically controlled by the ratio of cholesterol to phospholipids. In a low concentration of cholesterol A beta prefers to stay in membrane surface region mainly in a beta-sheet structure. In contrast, as the ratio of cholesterol to phospholipids rises above 30 mol%, A beta can insert spontaneously into lipid bilayer by its C terminus. During membrane insertion A beta generates about 60% alpha-helix and removes almost all beta-sheet structure. Fibril formation experiments show that such membrane insertion can reduce fibril formation. Our findings reveal a possible pathway by which A beta prevents itself from aggregation and fibril formation by membrane insertion.

1,2-Dipalmitoylphosphatidylcholine↗