Haimov, E. | bioRxiv Science

bioRxiv2021

An engineered nanocomplex with Photodynamic and Photothermal synergistic properties for cancer treatment

Photodynamic therapy (PDT) and photothermal therapy (PTT) are promising therapeutic methods for cancer treatment; however, as single modality therapies, either PDT or PTT are still limited in their success rate. A dual application of both PDT and PTT, in a combined protocol, has gained immense interest. In this study, gold nanoparticles (AuNPs) are conjugated with a PDT agent, meso-tetrahydroxyphenylchlorin (mTHPC) photosensitizer, designed as nanotherapeutic agents that can activate a dual photodynamic/photothermal therapy. The AuNP-mTHPC complex is biocompatible, soluable, and photostable. PDT efficiency is high because of immediate reactive oxygen species (ROS) production upon mTHPC activation by the 650 nm laser which decreased mitochondrial membrane potential ({Delta}{Psi}m). Likewise, the AuNP-mTHPC complex is used as a photoabsorbing (PTA) agent for PTT, due to efficient plasmon absorption and excellent photothermal conversion characteristics of AuNPs under laser irradiation at 532 nm. Under the laser irradiation of a PDT/PTT combination, a twofold phototoxicity outcome follows, compared to PDT-only or PTT-only treatment. This indicates that PDT and PTT have synergistic effects together as a combined therapeutic method. Hence, applying our AuNP-mTHPC may be a potential treatment of cancer in the biomedical field. O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=122 SRC="FIGDIR/small/471725v1_ufig1.gif" ALT="Figure 1"> View larger version (31K): org.highwire.dtl.DTLVardef@55fe3corg.highwire.dtl.DTLVardef@1a6468dorg.highwire.dtl.DTLVardef@161ea64org.highwire.dtl.DTLVardef@1638c91_HPS_FORMAT_FIGEXP M_FIG C_FIG

bioengineering↗

bioRxiv2021

Structural basis for long-chain isoprenoids synthesis by cis-prenyltransferases

Isoprenoids are the largest group of natural products, found in all living organisms and play an essential role in numerous cellular processes. These compounds are synthesized by prenyltransferases, catalyzing the condensation reaction between an allylic diphosphate primer and a variable number of isopentenyl diphosphate (C5) units. This superfamily of enzymes can be subdivided into trans- or cis-prenyltransferases according to the stereoisomerism of the product. The cis branch can be further classified according to product length. While the active site volume was suggested to determine the final length in enzymes synthesizing short- and medium-chain products (up to C60), long-chain enzymes (up to C120) and rubber synthases (>C10,000) fail to conform to this paradigm. Here, to resolve the structural basis for long-chain isoprenoid synthesis, we focused on the human cis-prenyltransferase complex (hcis-PT). This enzyme, peripheral to the endoplasmic reticulum membrane, produces the precursor for dolichol phosphate, a membrane residing glycosyl carrier. In line with its crucial role in the cellular protein glycosylation machinery, disease-causing mutations in hcis-PT were shown to result in a wide spectrum of clinical phenotypes. The crystallographic structures of hcis-PT in four different substrate/product-bound conformations revealed an outlet enabling product elongation into the bulk solvent. Moreover, hydrogen-deuterium exchange mass spectrometry analysis in solution showed that the hydrophobic active site core is flanked by dynamic regions consistent with separate inlet and outlet orifices. Finally, using a fluorescent substrate analog and a fluorescently-labeled lipid nanodiscs, we show that product elongation and membrane association are closely correlated. Together, our results support directional product synthesis in long-chain enzymes and rubber synthases, with a distinct substrate inlet and product outlet, allowing direct membrane insertion of the elongating isoprenoid during catalysis. This mechanism uncouples active site volume from product length and circumvents the need to expulse hydrophobic product into a polar environment prior to membrane insertion.

biochemistry↗