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Published July 16, 2018 | Published + Supplemental Material
Journal Article Open

Small near-infrared photochromic protein for photoacoustic multi-contrast imaging and detection of protein interactions in vivo


Photoacoustic (PA) computed tomography (PACT) benefits from genetically encoded probes with photochromic behavior, which dramatically increase detection sensitivity and specificity through photoswitching and differential imaging. Starting with a DrBphP bacterial phytochrome, we have engineered a near-infrared photochromic probe, DrBphP-PCM, which is superior to the full-length RpBphP1 phytochrome previously used in differential PACT. DrBphP-PCM has a smaller size, better folding, and higher photoswitching contrast. We have imaged both DrBphP-PCM and RpBphP1 simultaneously on the basis of their unique signal decay characteristics, using a reversibly switchable single-impulse panoramic PACT (RS-SIP-PACT) with a single wavelength excitation. The simple structural organization of DrBphP-PCM allows engineering a bimolecular PA complementation reporter, a split version of DrBphP-PCM, termed DrSplit. DrSplit enables PA detection of protein–protein interactions in deep-seated mouse tumors and livers, achieving 125-µm spatial resolution and 530-cell sensitivity in vivo. The combination of RS-SIP-PACT with DrBphP-PCM and DrSplit holds great potential for noninvasive multi-contrast deep-tissue functional imaging.

Additional Information

© 2018 The Author(s). This article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. The images or other third party material in this article are included in the article's Creative Commons license, unless indicated otherwise in a credit line to the material. If material is not included in the article's Creative Commons license and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this license, visit http://creativecommons.org/licenses/by/4.0/. Received: 13 September 2017 Accepted: 15 June 2018. Published online: 16 July 2018. We thank J. Ihalainen (University of Jyväskylä, Finland) for the DrBphP gene and E. Giraud (Institute for Research and Development, France) for the RpBphP1 gene. We also thank P. Zhang and T. Imai for technical support and J. Ballard for technical editing of the manuscript. This work was sponsored by the NIH grants EB016986 (Pioneer Award), CA186567 (Transformative Research Award), NS090579, NS099717, EB016963 (all to L.V.W.), GM122567, NS099573, NS103573, and the EU FP7 grant ERC-2013-ADG-340233 (all to V.V.V.). These authors contributed equally: Lei Li, Anton A. Shemetov, Mikhail Baloban. Author Contributions: V.V.V. conceived the study. L.L., A.A.S., M.B., L.V.W. and V.V.V. designed the experiments. A.A.S., M.B. and D.M.S. constructed the plasmids, characterized the purified proteins, and established the stable cell lines. L.L. and J.S. constructed the RS-SIP-PACT system. L.L. performed the photoacoustic experiments. L.L., P.H. and L.Z. analyzed the photoacoustic data. L.L. and R.Z. cultured the mammalian cells. L.V.W. and V.V.V. supervised the study. L.L., A.A.S., L.V.W. and V.V.V. wrote the manuscript. All authors reviewed the manuscript. Data availability: The data that support the findings of this study are available from the corresponding authors on reasonable request. The reconstruction algorithm and data processing methods are described in detail in the Methods. We have opted not to make the data acquisition, image reconstruction, and processing code available because the code is proprietary and used for other projects. Competing interests: L.V.W. has financial interests in Microphotoacoustics, Inc., CalPACT, LLC, and Union Photoacoustic Technologies, Ltd., which, however, did not support this work. The remaining authors declare no competing interests.

Attached Files

Published - s41467-018-05231-3.pdf

Supplemental Material - 41467_2018_5231_MOESM1_ESM.pdf

Supplemental Material - 41467_2018_5231_MOESM2_ESM.pdf

Supplemental Material - 41467_2018_5231_MOESM3_ESM.mp4

Supplemental Material - 41467_2018_5231_MOESM4_ESM.mp4

Supplemental Material - 41467_2018_5231_MOESM5_ESM.mp4

Supplemental Material - 41467_2018_5231_MOESM6_ESM.mp4


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