Charting the sequence-activity landscape of peptide inhibitors of translation termination.

Apidaecin (Api), an unmodified 18-amino-acid-long proline-rich antibacterial peptide produced by bees, has been recently described as a specific inhibitor of translation termination. It invades the nascent peptide exit tunnel of the postrelease ribosome and traps the release factors preventing their recycling. Api binds in the exit tunnel in an extended conformation that matches the placement of a nascent polypeptide and establishes multiple contacts with ribosomal RNA (rRNA) and ribosomal proteins. Which of these interactions are critical for Api's activity is unknown. We addressed this problem by analyzing the activity of all possible single-amino-acid substitutions of the Api variants synthesized in the bacterial cell. By conditionally expressing the engineered api gene, we generated Api directly in the bacterial cytosol, thereby bypassing the need for importing the peptide from the medium. The endogenously expressed Api, as well as its N-terminally truncated mutants, retained the antibacterial properties and the mechanism of action of the native peptide. Taking advantage of the Api expression system and next-generation sequencing, we mapped in one experiment all the single-amino-acid substitutions that preserve or alleviate the on-target activity of the Api mutants. Analysis of the inactivating mutations made it possible to define the pharmacophore of Api involved in critical interactions with the ribosome, transfer RNA (tRNA), and release factors. We also identified the Api segment that tolerates a variety of amino acid substitutions; alterations in this segment could be used to improve the pharmacological properties of the antibacterial peptide.

A Comprehensive Method to Measure 3-Dimensional Bra Motion During Physical Activity.

Breast and bra motion research aims to understand how the breasts/bra move to aid development of apparel that minimizes motion. Most previously published research has tracked nipple motion to represent bra motion. However, this method does not provide information regarding regional tissue motion. A more comprehensive approach might facilitate understanding how the entire soft-tissue mass moves during physical activities. This study developed and tested an objective method to comprehensively measure 3-dimensional bra motion, including regional displacement and velocity, displacement phasing, and surface stretch. To test the method, 6 females were fitted with a minimally supportive, seamless bra (small bra n = 3; large bra n = 3). Data were collected as participants ran on a treadmill. Results indicated marker displacement, velocity, link stretch, and link stretch velocities reached as high as 52.6 (6.8) mm, 504.8 (88.7) mm/s, 29.5% (7.1%) of minimum length, and 3.8 (1.0) mm/s/mm, respectively, with the large bra having greater motions compared with the small. Most bra motion occurred above/below the nipple region and at the bra's strap-body interface, independent of bra size. Importantly, maximum marker displacement and velocity did not occur at the nipple. Measurements obtained from this new method may be important for designing innovative clothing that minimizes bra motion during physical activity.

Evaluating the relationship between gait and clinical measures of plantar flexor function.

Individuals with plantar flexor weakness often require rehabilitation and/or orthoses, which should be personalized based on level of weakness. While plantar flexor weakness can be measured via peak plantar flexion moment during gait (MGAIT), motion analysis systems are often not clinically available. Clinical measures, such as the single-leg heel rise (SLHR) test and isometric muscle test, may provide surrogate measures of plantar flexor function during gait. However, it is currently unknown if a relationship(s) exists between such measures. This study evaluated the relationship between gait and clinical measures of plantar flexor function for typical individuals. Twenty-four participants underwent an instrumented gait analysis, from which MGAIT was calculated. Next, participants performed an isometric plantar flexor test, from which the maximum plantar flexion moment (MISO) was calculated. Finally, participants performed a SLHR test, from which maximum plantar flexion moment (MSLHR) and total work (Wtot_SLHR) were calculated. Via Pearson correlations, MSLHR was most strongly correlated to MGAIT (r = 0.56; p = 0.005). Wtot_SLHR was significantly correlated to MGAIT (r = 0.47; p = 0.019). MISO was not significantly correlated to MGAIT (r = 0.19; p = 0.363). MSLHR and/or Wtot_SLHR may provide clinically-feasible surrogate measures of plantar flexor function during gait.