Eunhye Park

Phosphorylation of Stargazin by Protein Kinase A Regulates Its Interaction with PSD-95

Stargazin is the first transmembrane protein known to associate with AMPA (α-amino-3-hydroxy-5-methylisoxazole-4-propionate) glutamate receptors (AMPARs) and regulate their synaptic targeting by two distinct mechanisms, specifically via delivery of AMPARs to the surface membrane and synaptic targeting of these receptors by binding to PSD-95/SAP-90 and related PDZ proteins. However, it is not known whether and how this stargazin-mediated synaptic targeting of AMPARs is regulated. Stargazin interacts with the PDZ domains of PSD-95 through the C-terminal PDZ-binding motif. The stargazin C terminus contains a consensus sequence for phosphorylation by cAMP-dependent protein kinase A (PKA). Phosphorylation site-specific stargazin antibodies reveal that the stargazin C terminus is phosphorylated at the Thr-321 residue in heterologous cells and in vivo. Stargazin phosphorylation is enhanced by the catalytic subunit of PKA. Mutations mimicking stargazin phosphorylation (T321E and T321D) lead to elimination of yeast two-hybrid interactions, in vitrocoimmunoprecipitation, and coclustering between stargazin and PSD-95. Phosphorylated stargazin shows a selective loss of coimmunoprecipitation with PSD-95 in heterologous cells and limited enrichment in postsynaptic density fractions of rat brain. These results suggest that phosphorylation of the stargazin C terminus by PKA regulates its interaction with PSD-95 and synaptic targeting of AMPARs.

SHN‐1, a Shank homologue in C. elegans, affects defecation rhythm via the inositol‐1,4,5‐trisphosphate receptor

Protein localization in the postsynaptic density (PSD) of neurons is mediated by scaffolding proteins such as PSD‐95 and Shank, which ensure proper function of receptors at the membrane. The Shank family of scaffolding proteins contain PDZ (PSD‐95, Dlg, and ZO‐1) domains and have been implicated in the localizations of many receptor proteins including glutamate receptors in mammals. We have identified and characterized shn‐1, the only homologue of Shank in Caenorhabditis elegans. The shn‐1 gene shows approximately 40% identity over 1000 amino acids to rat Shanks. SHN‐1 protein is localized in various tissues including neurons, pharynx and intestine. RNAi suppression of SHN‐1 did not cause lethality or developmental abnormality. However, suppression of SHN‐1 in the itr‐1 (sa73) mutant, which has a defective inositol‐1,4,5‐trisphosphate (IP3) receptor, resulted in animals with altered defecation rhythm. Our data suggest a possible role of SHN‐1 in affecting function of IP3 receptors in C. elegans.

Identification of Non-Ideal Receiver Condition for Orbital Angular Momentum Transmission

Although orbital angular momentum (OAM) was first introduced for optical communications, it is drawing attention as a new transmission technique for millimeter wave communication. Due to the additional orthogonal transmit dimension by photon OAM, the theoretical throughput can increase dramatically with various OAM modes. In practice, since OAM by uniform circular arrays (UCAs) has the implementation problem such as twisted axis between transmitter and receiver, the performance degradation happens frequently. Hence, this paper investigates the imperfect receiver condition and the effect of this problem. In particular, the off-axis and non-parallel location problems are focused. Here, the capacity with inter-mode interference (IMI) of OAM is first considered and the receiver compensation method is proposed. Numerical results show that the throughput after compensation is better than that without compensation.

Location-Based Initial Access and Beam Adaptation for Millimeter Wave Systems

This paper proposes optimal beam adaptation (BA) and initial access (IA) algorithms for millimeter wave (mmWave) uplink systems, which make use of the estimated location of user equipment (UE) by access points (APs) rather than using exhausting full beam sweep for the beam direction toward UEs. Based on the location estimation, the optimal beamwidth guaranteeing the highest connection probability is derived for the optimal BA method. The proposed IA procedure selects the best AP not only based on the channel gain but also based on the location estimation, which leads to reduce the outage probability of cell-edge users. Numerical evaluation shows that both BA and IA outperform the conventional procedure in terms of of average achievable rate for the cell edge users, when separately applied. Numerical results are also provided with better performance than conventional systems without BA and IA suggested, for the case when both BA and IA are applied.

Performance analysis of pulse designed for the IEEE 802.15.4a standard

The novel pulses, which not only meet the power spectral mask of the Federal Communications Commission(FCC) and IEEE 802.15.4a standard constraint but also preserve the orthogonality at the receiver, have been proposed by Kim et. al. for practical usage of Ultra-wideband (UWB) system. This paper analyzes the performance of proposed pulses with regards important conditions in UWB system, such as the standard constraints, spectral utilization efficiency, capacity and effect on multipath fading with different existing pulses. Simulation results demonstrate the performance analysis of the proposed pulses.