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Complementing X-Ray, NMR, Swedish Sidec Maps Frozen Proteins in Three Dimensions


One limitation of X-ray crystallography and NMR is that the structures they produce don’t always reflect what proteins look like in the cell. Swedish biotech startup Sidec Technologies promises to solve this problem — and contribute to drug discovery — by applying electron microscopy to imaging of proteins in three dimensions. Last week, the Stockholm-based company received a boost for its efforts, announcing additional funding of 10 million krona ($1.3 million) from Industrifonden, the Swedish Industrial Development Fund.

Sidec uses electron tomography, where a three-dimensional image is reconstructed from a series of two-dimensional ones. In a nutshell, scientists collect images from frozen tissues, cells, or proteins in solution at different angles by electron microscopy, using low doses of electrons, and reconstruct three-dimensional shapes of individual proteins or protein complexes at down to two nanometer resolution using a patented algorithm. “Our sample is like a frozen aquarium,” said Gösta Sjöholm, the company’s CEO. “You can analyze and study each individual fish in that aquarium.”

Part of the new funding from Industrifonden — which also took a 14 percent ownership in the company — will go towards hiring more scientists to develop applications, such as epitope mapping of antibodies, and to increase capacity for collaborations. The funding adds to almost $3 million the company raised in the past. The Karolinska Investment Fund is the main investor.

Sidec, founded in the spring of 2000, is a spin-off from the Karolinska Institute in Stockholm, where Ulf Skoglund, a professor in the department of cell and molecular biology, developed a patented algorithm called Comet, short for Constrained Maximum Entropy Tomography. According to Sjöholm, two aspects of this iterative algorithm allow for the reconstruction of high-resolution images: It improves the fit of the experimental data with the model with every iteration, and it removes experimental noise “so we end up with a noise-free image in the end.”

The main advantage of the technology is that it is able to look at individual proteins in solution, or even in the context of a cell or tissue. For example, individual membrane receptors — including their transmembrane and intracellular region — can be studied in a tissue, where they are identified by gold-labeled antibodies. However, the technique does not reach atomic resolution, and individual molecules cannot be smaller than 10 kDa.

Sjöholm sees two initial applications for the technology in drug discovery: It may help users evaluate cell-based assays for studying membrane receptors by enabling comparisons of their stoichiometry and conformation in tissue to that in the assay. “If the conformation or stoichiometry is different, you will probably get another function from the potential drug than you expect,” Sjöholm said. “If you develop drugs on a faulty model, you will get faulty drug actions.” Secondly, the technology may assist during lead optimization, for example to clarify how a hormone binds to its receptor, or how a drug disrupts protein-protein interactions.

Sidec has used the technology to visualize the interaction between human growth hormone and its receptor. Its researchers have also studied glycosylation sites on a protein, using lectin — a sugar-binding protein — as a marker.

The company, which has about 10 employees, is housed in the Karolinska Science Park and is equipped with one rented electron microscope, as well as computers and visualization tools. It is offering contract protein characterization services to biotechnology and pharmaceutical companies and has established almost 10 collaborations so far, with Biovitrum, Bioinvent, Amersham Biosciences, Procognia, the Cleveland Clinic Foundation, and several undisclosed pharmaceutical companies, according to Sjöholm. By the end of the year, Sidec is “hoping to get closer to break-even,” a goal it wants to achieve next year.

— JK

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