Kai Johnson - Academia.edu (original) (raw)

Papers by Kai Johnson

Scholarship and Practice of Undergraduate Research

European Archives of Oto-Rhino-Laryngology

The objective of this manuscript is to review a single institution's experience with supe... more The objective of this manuscript is to review a single institution's experience with superficial or total parotidectomy in outpatient and observation/inpatient groups. All patients who underwent superficial or total parotidectomy between 2009 and 2015 were identified. Patients were excluded if they had undergone concurrent surgery such as neck dissection, had prior radiation treatment or surgery at the operative site. Main outcomes were perioperative complications in both groups. 215 consecutive patients were included in the study, 116 (54%) patients in the inpatient group and 99 (46%) in the outpatient group. Aside from a higher observed rate of cardiac disease in the outpatient group (24.2 vs. 11.2%, p = 0.014) and larger mean body mass index (BMI) in the inpatient group (32.448 vs. 30.034, p = 0.017), there were no significant differences for age, sex or smoking status. Average operative time differed between groups with 2 h 42 min for inpatients and 2 h 18 min for outpatients (p < 0.001). There were 26 complications in the inpatient group (22.4%, including two hematomas) and 8 in the outpatient group (8.1%). The rate of seroma/sialocele formation was significantly higher in the inpatient group at 15.5% (n = 18) compared with the outpatient group at 3% (n = 3, p = 0.001). Our study shows that parotidectomy, superficial or total, was performed safely as an outpatient procedure without significant increase in complications when compared to patients observed for at least one night after surgery.

GBM Annual Spring meeting Mosbach 2003, 2003

Proceedings of the National Academy of Sciences, 2013

Proceedings of the National Academy of Sciences, 2006

Molecular Microbiology, 2008

Protein kinase G of Mycobacterium tuberculosis has been implicated in virulence and in regulation... more Protein kinase G of Mycobacterium tuberculosis has been implicated in virulence and in regulation of glutamate metabolism. Here we show that this kinase undergoes a pattern of autophosphorylation that is distinct from that of other M. tuberculosis protein kinases characterized to date and we identify GarA as a substrate for phosphorylation by PknG. Autophosphorylation of PknG has little effect on kinase activity but promotes binding to GarA, an interaction that is also detected in living mycobacteria. PknG phosphorylates GarA at threonine 21, adjacent to the residue phosphorylated by PknB (T22), and these two phosphorylation events are mutually exclusive. Like the homologue OdhI from Corynebacterium glutamicum, the unphosphorylated form of GarA is shown to inhibit a-ketoglutarate decarboxylase in the TCA cycle. Additionally GarA is found to bind and modulate the activity of a large NAD +-specific glutamate dehydrogenase with an unusually low affinity for glutamate. Previous reports of a defect in glutamate metabolism caused by pknG deletion may thus be explained by the effect of unphosphorylated GarA on these two enzyme activities, which may also contribute to the attenuation of virulence.

Journal of the American Chemical Society, 2005

We report on a method for the multicolor imaging of cell surface proteins which is based on the l... more We report on a method for the multicolor imaging of cell surface proteins which is based on the labeling of carrier protein (CP) fusion proteins with different fluorophores. In one application, different generations of a cell surface protein can be sequentially labeled to discriminate between old and newly made copies. In another application, fusions to different CPs can be selectively labeled with different fluorophores in one sample. Both applications open up new ways for studying the properties of cell surface proteins of living cells.

Journal of Microbiological Methods, 2008

The study of protein function in living cells is an essential complement to genomics, yet method ... more The study of protein function in living cells is an essential complement to genomics, yet method development does not always keep pace with sequencing. Experimental techniques for the genus mycobacteria are relatively underdeveloped, though seventeen genomes have been sequenced. "Split-Trp" is a split-protein sensor used to detect protein-protein interactions in tryptophan auxotrophic Saccharomyces cerevisiae, but the principles behind the sensor should allow it to function in a broad range of microbial hosts. Here we introduce Split-Trp to Escherichia coli and Mycobacterium smegmatis and demonstrate that this system is a simple assay for protein interaction in both organisms.

Chemistry & Biology, 2008

The visualization of complex cellular processes involving multiple proteins requires the use of s... more The visualization of complex cellular processes involving multiple proteins requires the use of spectroscopically distinguishable fluorescent reporters. We have previously introduced the SNAP-tag as a general tool for the specific labeling of SNAP-tag fusion proteins in living cells. The SNAP-tag is derived from the human DNA repair protein O 6-alkylguanine-DNA alkyltransferase (AGT) and can be covalently labeled in living cells using O 6-benzylguanine derivatives bearing a chemical probe. Here we report the generation of an AGT-based tag, named CLIPtag, which reacts specifically with O 2-benzylcytosine derivatives. Because SNAP-tag and CLIP-tag possess orthogonal substrate specificities, SNAP and CLIP fusion proteins can be labeled simultaneously and specifically with different molecular probes in living cells. We furthermore show simultaneous pulsechase experiments to visualize different generations of two different proteins in one sample.

Analytica Chimica Acta, 2012

h i g h l i g h t s Color tunable materials on a QCM crystal can detect solution pH changes. Sens... more h i g h l i g h t s Color tunable materials on a QCM crystal can detect solution pH changes. Sensitivity of 1.3 × 10 −8 M [H + ] Hz −1 is achieved over a 2 pH unit range. Detection limit of 390 nM [H + ] was realized.

ACS Chemical Biology, 2006

We introduce a strategy for evolving protein substrate specificity by the insertion of random ami... more We introduce a strategy for evolving protein substrate specificity by the insertion of random amino acid loops into the protein backbone. Application of this strategy to human O6-alkylguanine-DNA alkyltransferase (AGT) led to the isolation of mutants that react with the non-natural substrate O6-propargylguanine. Libraries generated by conventional random or targeted saturation mutagenesis, by contrast, did not yield any mutants with activity towards this new substrate. The strategy of loop insertion to alter enzyme specificity should be general and applicable to other classes of proteins. An important application of the isolated AGT mutant is in molecular imaging, where the mutant and parental AGTs are used to label two different AGT fusion proteins with different fluorophores in the same living cell or in vitro . This allowed the establishment of fluorescence-based assays to detect protein-protein interactions and measure enzymatic activities.