Nature utilizes photosensory proteins to allow cells to detect changes in light and react accordingly. We’ve focused our attention on two classes of such proteins which use flavin chromophores – FMN, FAD, or riboflavin – to detect changes in blue light, asking how photochemical changes at these cofactors are amplified by the surrounding proteins to achieve biochemical change. We’ve done most of this work in Light-Oxygen-Voltage (LOV) domains, starting from NMR studies of a plant phototropin LOV domain to determine how such changes control the structure of a part (“Jα helix”) that in turn controls enzymatic activity of this protein (Harper 2003, Harper 2004a, Harper 2004b). From this start, we’ve investigated similar changes in diverse full-length proteins – from bacterial histidine kinases (Correa 2013, Rivera-Cancel 2014, Dikiy 2019) and transcription factors (He 2002, Nash 2011, Zoltowski 2011, Rivera-Cancel & Motta-Mena 2012) to fungal controllers of G protein signaling (Glantz 2016, Glantz 2018) – to ask what elements are common among these proteins and which are different, and how these changes affect function in vitro and in living cells.
From this work, we’ve turned some natural photosensors into very useful ontogenetic tools, including one (EL222) that can turn genes on in a wide range of cell types using blue light (Motta-Mena 2014, Reade 2017, LaBelle 2021), leading to a spin-off company named Optologix. This work has also helped inspire a range of protein engineering applications in many labs where LOV domains are fused into proteins which aren’t normally light sensitive, turning them into new reagents for biotechnology (Losi 2018, and nicely surveyed by the hard working team at OptoBase). We’ve pursued a combination of approaches to make LOV domains better photosensors as part of this, too (Yao 2008, Strickland 2010, Song 2011, Freddolino 2013)
Complementing this work, we’ve also studied Blue Light sensors Utilizing Flavins (BLUF), which use similar chromophores and protein structures, but different photochemistry from the LOV domains. NMR and biochemical studies from our lab and others have shown similar structural changes as the LOV domains, albeit in ways that are different in some important ways (Jung 2005, Wu 2008, Wu 2009, Yuan 2011).