Daniel Branton

Daniel Branton (born January 13, 1932) is an American cell biologist. He is the Higgins Professor of Biology, Emeritus, at Harvard University.^[1] In the 1960s he worked out why electron micrographs of frozen cells show the inside of membranes, which gave strong evidence that biological membranes are built on a lipid bilayer. In the 1990s he joined David Deamer and others in the experiments that showed single strands of nucleic acid could be read as they passed through a protein pore, work that led to nanopore sequencing.

In 1961 Branton began a two-year postdoctoral fellowship from the National Science Foundation in Zurich, in the department of Albert Frey-Wyssling at the ETH, where he worked with Fritz Ruch. He decided that the hypothesis behind his project was misguided, and Ruch persuaded him to spend a few months showing carefully why earlier investigators' data had misled them. The tedium, he wrote later, "motivated me to find a project that would open new insights rather than simply falsify a hypothesis".^[2]

The alternative was a method being developed down the corridor by Hans Moor. Freeze-etching, begun by Russell Steere, froze a specimen quickly in a block of ice, planed the ice away with a scalpel and made a metal replica of the exposed surface to view in the electron microscope. It needed no chemical fixation or embedding. Branton used it on onion root tips and found particles 7 to 10 nm across on most membrane faces, which Moor took for ribosomes.^[2] Back in California as a new assistant professor at Berkeley, Branton reexamined his replicas and noticed a small ridge at the base of every exposed membrane face. Where a face curved into a cross-section, the ridge joined the membrane's edge. He concluded that the fracture runs through the middle of the membrane and splits it into two halves, so that the faces in the micrographs are interior faces, never the outer surfaces. His paper "Fracture faces of frozen membranes" appeared in the Proceedings of the National Academy of Sciences in May 1966.^[3]

At that year's meeting of the American Society for Cell Biology in Houston the interpretation met skepticism. Richard McIntosh, then a Harvard student, politely explained his doubts and left with the words "Dan, why don't you do an experiment?" By the time Branton's flight landed in California he had designed one, in which a lipid bilayer labeled with carbon-14 would be frozen and fractured on a glass slide, and he asked around for someone who could make such layers. David Deamer, a new postdoctoral fellow in a neighboring laboratory, was the one who knew how. Using carbon-14 stearic acid, a toy jack and other improvised equipment they showed that frozen stearate bilayers cleave in the plane between the hydrocarbon tails.^[2][4] At Deamer's suggestion they also timed how fast label moved between the two layers before freezing. The half-time was 50 minutes with calcium present and 25 minutes without, the first demonstration of lipid flip-flop.^[4]

The particles on the faces were later shown to be transmembrane proteins, by reconstituting a red blood cell protein into lipid vesicles and finding the same particles after freeze-fracture.^[5]

Branton moved from Berkeley to Harvard. His laboratory stayed on the red blood cell, studying the network of spectrin and actin that lines the inner face of its membrane.^[6] He held a Guggenheim Fellowship in 1970 and was elected to the National Academy of Sciences in 1981.^[7] The American Academy of Arts and Sciences elected him in 1974, and he was president of the American Society for Cell Biology in 1985.^[8][9]

In 1991 Branton visited Deamer at the University of California, Davis, to give a series of lectures. He had been thinking about the methods then in use for sequencing DNA and, by the Golden Goose Award's account, told himself "There must be a better way of doing this." His own idea was to measure the force needed to pull each base of a single strand through the interface between water and air. Deamer showed him a notebook page in which a voltage drove a strand through a channel and each base changed the current. Branton agreed that the notebook idea was better.^[10]

A patent application filed on March 17, 1995 names Branton with George Church, Deamer, Richard Baldarelli and John Kasianowicz.^[11] The paper by Kasianowicz, Eric Brandin, Branton and Deamer, which reported single strands of RNA passing through a pore of alpha-hemolysin, was published in November 1996. The Golden Goose account adds that Branton's membership in the National Academy of Sciences helped it into the Proceedings.^[12][10]

At Harvard, Branton worked with the physicist Jene Golovchenko on holes in solid materials. Their 2001 paper described "ion-beam sculpting", a feedback-controlled method that uses low-energy ion beams to shape a molecular-scale hole in a silicon nitride membrane, and a pore made this way that registered single DNA molecules.^[13] In 2007 Branton, Deamer, Mark Akeson and Golovchenko agreed to license their patents to Oxford Nanopore Technologies, which brought out the MinION seven years later.^[10] A review he wrote in 2008 with Deamer, Marziali, Bayley and others surveyed the promise of nanopore sequencing, with a solid-state nanopore or a biological nanopore, and what stood in its way.^[14]

In 2016 Deamer, Akeson and Branton published a history, "Three decades of nanopore sequencing", which drew a published reply from Kasianowicz and Sergey Bezrukov disputing parts of it; the two accounts are compared in History of nanopore sequencing.^[15] In 2023 the Golden Goose Award, which honors federally funded research that seemed obscure at the start, went to Branton, Deamer and Akeson.^[10][1]

• David Deamer
• Nanopore
• Wallace H. Coulter