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ToxR-based transcriptional reporter assays allow the strength of transmembrane helix interactions in biological membranes to be measured. Previously, these assays have only been used to study single-pass transmembrane systems. To facilitate investigation of polytopic transmembrane domain (TMD) oligomerization, we applied the ToxR methodology to the study of multi-pass TMD oligomerization to give ‘Multi-Tox’. Association propensities of the viral oncoprotein, latent membrane protein-1 (LMP-1), and the E. coli membrane-integral diacylglycerol kinase (DAGK) were studied by Multi-Tox, highlighting residues of particular mechanistic importance. Both homo- and hetero-oligomerizations were studied.

ImportanceAlthough longer times from breast cancer diagnosis to primary surgery have been associated with worse survival outcomes, the specific time point after which it is disadvantageous to have surgery is unknown. Identifying an acceptable time to surgery would help inform patients, clinicians, and the health care system.ObjectiveTo examine the association between time from breast cancer diagnosis to surgery (in weeks) and overall survival and to describe factors associated with surgical delay. The hypothesis that there is an association between time to surgery and overall survival was tested.Design, Setting, and ParticipantsThis was a case series study that used National Cancer Database (NCDB) data from female individuals diagnosed with breast cancer from 2010 to 2014 (with 5-year follow-up to 2019). The NCDB uses hospital registry data from greater than 1500 Commission on Cancer–accredited facilities, accounting for 70% of all cancers diagnosed in the US. Included participants were females 18 years or older with stage I to III ductal or lobular breast cancer who underwent surgery as the first course of treatment. Patients with prior breast cancer, missing receptor information, neoadjuvant or experimental therapy, or who were diagnosed with breast cancer on the date of their primary surgery were excluded. Multivariable Cox regression was used to evaluate factors associated with overall survival. Patients were censored at death or last follow-up. Covariates included age and tumor characteristics. Multinomial regression was performed to identify factors associated with longer time to surgery, using surgery 30 days or less from diagnosis as the reference group. Data were analyzed from March 15 to July 7, 2022.ExposuresTime to receipt of primary breast surgery.MeasuresThe primary outcome measure was overall survival.ResultsThe final cohort included 373 334 patients (median [IQR] age, 61 [51-70] years). On multivariable Cox regression analysis, time to surgery 9 weeks (57-63 days) or later after diagnosis was associated with worse overall survival (hazard ratio, 1.15; 95% CI, 1.08-1.23; P < .001) compared with surgery between 0 to 4 weeks (1-28 days). By multinomial regression, factors associated with longer times to surgery (using surgery 1-30 days from diagnosis as a reference) included the following: (1) younger age, eg, the adjusted odds ratio (OR) for patients 45 years or younger undergoing surgery 31 to 60 days from diagnosis was 1.32 (95% CI, 1.28-1.38); 61 to 74 days, 1.64 (95% CI, 1.52-1.78); and greater than 74 days, 1.58 (95% CI, 1.46-1.71); (2) uninsured or Medicaid status, eg, the adjusted OR for patients with Medicaid undergoing surgery 31 to 60 days from diagnosis was 1.35 (95% CI, 1.30-1.39); 61 to 74 days, 2.13 (95% CI, 2.01-2.26); and greater than 74 days, 3.42 (95% CI, 3.25-3.61); and (3) lower neighborhood household income, eg, the adjusted OR for patients with household income less than $38,000 undergoing surgery 31 to 60 days from diagnosis was 1.35 (95% CI, 1.02-1.07); 61 to 74 days, 1.21 (95% CI, 1.15-1.27); and greater than 74 days, 1.53 (95% CI, 1.46-1.61).Conclusions and RelevanceFindings of this case series study suggest the use of 8 weeks or less as a quality metric for time to surgery. Time to surgery of greater than 8 weeks may partly be associated with disadvantageous social determinants of health.

The oversimplified view of protein transmembrane domains as merely anchors in phospholipid bilayers has long since been disproven. In many cases membrane-spanning proteins have evolved highly sophisticated mechanisms of action. [1][2][3] One way in which membrane proteins can modulate their structures and functions is by direct and specific contact of hydrophobic helices, forming structured transmembrane oligomers. 4,5 Much recent work has focused on the distribution of amino acids preferentially found in the membrane environment in comparison to aqueous solution and the different intermolecular forces that drive protein association. 6,7 Nevertheless, studies of molecular recognition at the transmembrane domain of proteins still lags behind those of water-soluble regions. A major hurdle remains: despite the remarkable specificity and affinity that transmembrane oligomerization can achieve, 8 direct measurement of their association is challenging. Traditional methodologies applied to the study of integral membrane protein function can be hampered by the inherent insolubility of the sequences under examination. Biophysical insights gained from studying synthetic peptides representing transmembrane domains can provide useful structural insight. However, the biological relevance of the detergent micellar or liposome systems used in these studies to mimic cellular membranes is often questioned; do peptides adopt a native-like structure under these conditions and does their functional behaviour truly reflect the mode of action within a native membrane? In order to study the interactions of transmembrane sequences in natural phospholipid bilayers, the Langosch lab developed ToxR transcriptional reporter assays. 9 The transmembrane domain of interest is expressed as a chimeric protein with maltose binding protein for location to the periplasm and ToxR to provide a report of the level of oligomerization (Figure 1).In the last decade, several other groups (e.g. Engelman, DeGrado, Shai) further optimized and applied this ToxR reporter assay. [10][11][12][13] The various ToxR assays have become a gold standard to test protein-protein interactions in cell membranes. We herein demonstrate a typical experimental operation conducted in our laboratory that primarily follows protocols developed by Langosch. This generally applicable method is useful for the analysis of transmembrane domain self-association in E. coli, where β-galactosidase production is used to assess the TMD oligomerization propensity. Upon TMD-induced dimerization, ToxR binds to the ctx promoter causing up-regulation of the LacZ gene for β-galactosidase. A colorimetric readout is obtained by addition of ONPG to lyzed cells. Hydrolytic cleavage of ONPG by β-galactosidase results in the production of the light absorbing species o-nitrophenolate (ONP) (Figure 2). Video LinkThe video component of this article can be found at http://www.jove.com/details.php?id=2721 Protocol Cloning ConsiderationsThe TMD sequence should be 12-24 residues (shorter sequences wi...

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