Harold Paul Erickson
James B. Duke Professor of Cell Biology

Cytoskeleton: It is now clear that the actin and microtubule cytoskeleton originated in bacteria. Our major research is on FtsZ, the bacterial tubulin homolog, which assembles into a contractile ring that divides the bacterium. We have studied FtsZ assembly in vitro, and found that it assembles into thin protofilaments (pfs). Dozens of these pfs are further clustered to form the contractile Z-ring in vivo. Some important discoveries in the last ten years include:

•    Reconstitution of Z rings in vitro. We provided FtsZ with a membrane tether, and found that when incorporated inside liposomes, FtsZ-mts can assemble Z rings without any other proteins.

•    These reconstituted Z rings generate a constriction force on the membranes, again without any other proteins (no motor molecules).

•    The constriction force is generated by a curved conformation of FtsZ pfs generating a bending force on the membrane.

Important questions for the future are:

  • How are FtsZ pfs arranged in the Z ring? We favor the ribbon model, where pfs are parallel and laterally associated into a ribbon. Many others in the field favor a scattered model, where pfs are more widely separated. We are exploring new electron microscopy (EM) methods to resolve the structure. We have also developed new tools to facilitate superresolution light microscopy (PALM).
  • How does FtsZ treadmilling work? Our lab provided the first evidence that FtsZ treadmills, adding subunits at one end and losing them at the other (Redick J Bact 2005). This has now been confirmed in vitro and in vivo. We are developing theoretical models and experimental (EM) methods to determine the detailed mechanism of treadmilling.
  • What is the structure of the septum in dividing bacteria? There is wide agreement that Gram-positive bacteria divide by ingression of a plate-like septum. Conventional EM suggests that Gram-negative bacteria have a shallower V-shaped constriction. We are revisiting this using novel fixatives and high-pressure freezing for thin section EM.
Irisin. We believe the irisin story is bunk. Irisin was proposed in 2012 as a novel myokine, secreted by muscle cells in response to exercise, it induces the transformation of white fat to brown fat. This inspired hopes of an exercise pill that might correct obesity and other metabolic disorders. We have argued that the original discovery was flawed in several respects (Erickson, Adipocyte, 2013), and that the 300+ published follow-up studies are based on flawed commercial antibodies (Albrecht et al, Sci Rep 2015). We are now developing new assays to determine if irisin exists in in the blood of humans, primates and other animals. We expect it does not, especially in humans whose FNDC5 gene has a mutated start codon.

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