Mesoscopic Adaptive Resolution Scheme toward understanding of interactions between sickle cell fibers

BPJ_113_1.c1.inddSickle cell disease (SCD) is a molecular disease that affects hemoglobin. To understand the altered morphologies and mechanical properties of sickle red blood cells in SCD, it is important to investigate polymerization of the mutated form of hemoglobin (HbS) and subsequent interaction with the red blood cell (RBC) membrane.

The cover image for the July 11 issue of the Biophysical Journal is an artistic rendering of several RBCs and a white blood cell in the blood flow. Some RBCs are sickle-like shape. The largest RBC in the bottom left corner is shown in the protein level. The red, blue, and green particles represent the lipid particles, spectrin proteins, and actin junctions in the RBC membrane, respectively. Inside the RBC,  a single HbS fiber consists of 14 chains of HbS tetramers arranged in a 7 double-stranded configuration. The 14 chains of HbS tetramers are twisted about a common axis in a rope-like fashion. In the image, one small yellow particle is one HbS molecule, and  56 small particles are coarse-grained as one large yellow particle.

As shown in the image, the proposed hybrid HbS fiber model seamlessly couples these two HbS fiber models at different length scales by applying a mesoscopic adaptive resolution scheme (MARS). The stiff HbS fibers interact with the RBC membrane and distort the RBC to the sickle shape. Sickle RBC morphologies are determined by the number of HbS fiber domains and the structure of each domain inside the cells. In return, the RBC membrane also suppresses the growth of the HbS fiber. In addition to irregular shapes, sickle RBCs are characterized by increased cell rigidity due to intracellular fiber structures, resulting in blood flow impairment and vaso-occlusive crises in the microcirculation.

This cover was inspired by the pressing need to understand the integrated process of HbS nucleation and polymerization, and subsequent alterations of cell morphology, which is a multi-scale process ranging from nanometers to micrometers. In order to accurately describe this process, the hybrid HbS fiber model is employed to capture the dynamic process of polymerization of HbS fibers, while maintaining the mechanical properties of polymerized HbS fibers, thus providing a means of bridging the subcellular and cellular phenomena in sickle cell disease.

—- Lu Lu, He Li, Xin Bian, Xuejin Li, and George Em Karniadakis


Nanoscale Optical Imaging


We appreciate the opportunity to illustrate a new powerful technique, Tip Enhanced Raman Spectroscopy (TERS) as cover art for the Biophysical Journal.  TERS, the combination of Atomic Force Microscopy (AFM) and Raman microscopy, provides chemical information with nanometer spatial resolution.  The cover image shows a TERS probe, a metal nano particle(s) mounted on an AFM tip, placed near an amyloid fibril.  A Raman signal is strongly enhanced in nanometer vicinity of the particle providing vibrational signature of the fibrillar surface.  Moving the cantilever allows for mapping the surface and providing structural information relevant to the biological activity and associated toxicity of the fibrils.

The application of TERS for structural characterization of biological species is a new, but quickly developing field.  The illustration of TERS on the cover of the Biophysical Journal is an important recognition of the power and uniqueness of this technique.  We hope this helps generate interest in TERS and attracts more researchers to this growing field.

–Dmitry Kurouski , Tanja Deckert-Gaudig , Volker Deckert, and Igor Lednev