title: Decomposing complete equipartite graphs into short even cycles

authors: Smith, Benjamin R.

subjects: graph decomposition

abstract: In this article we find necessary and sufficient conditions to decompose a complete equipartite graph into cycles of uniform length, in the case that the length is both even and short relative to the number of parts.

text: Decomposing complete equipartite graphs into short even cycles In this article we find necessary and sufficient conditions to decompose a complete equipartite graph into cycles of uniform length, in the case that the length is both even and short relative to the number of parts.

year: 2010

title: A structural basis for the reduced toxicity of dinophysistoxin-2

authors: Huhn, Jason

subjects: dinophysistoxin

abstract: Okadaic acid (OA), dinophysistoxin-1 (DTX-1), and dinophysistoxin-2 (DTX-2) are algal toxins that can accumulate in shellfish and cause diarrhetic shellfish poisoning. Recent studies indicate that DTX-2 is about half as toxic and has about half the affinity for protein phosphatase 2A (PP2A) as OA. NMR structural studies showed that DTX-1 possessed an equatorial 35-methyl group but that DTX-2 had an axial 35-methyl group. Molecular modeling studies indicated that an axial 35-methyl could exhibit unfavorable interactions in the PP2A binding site, and this has been proposed as the reason for the reduced toxicity of DTX-2. Statistical analyses of published data indicate that the affinity of PP2A for DTX-1 is 1.6-fold higher, and for DTX-2 is 2-fold lower, than for OA. We obtained X-ray crystal structures of DTX-1 and DTX-2 bound to PP2A. The crystal structures independently confirm the C-35 stereochemistries determined in the earlier NMR study. The structure for the DTX-1 complex was virtually identical to that of the OA-PP2A complex, except for the presence of the equatorial 35-methyl on the ligand. The favorable placement of the equatorial 35-methyl group of DTX-1 against the aromatic π-bonds of His191 may account for the increased affinity of PP2A toward DTX-1. In contrast, the axial 35-methyl of DTX-2 caused the side chain of His191 to rotate 140° so that it pointed toward the solvent, thereby opening one end of the hydrophobic binding cage. This rearrangement to accommodate the unfavorable interaction from the axial 35-methyl of DTX-2 reduces the binding energy and appears to be responsible for the reduced affinity of PP2A for DTX-2. These results highlight the potential of molecular modeling studies for understanding the relative toxicity of analogues once the binding site at the molecular target has been properly characterized.

text: A structural basis for the reduced toxicity of dinophysistoxin-2 Okadaic acid (OA), dinophysistoxin-1 (DTX-1), and dinophysistoxin-2 (DTX-2) are algal toxins that can accumulate in shellfish and cause diarrhetic shellfish poisoning. Recent studies indicate that DTX-2 is about half as toxic and has about half the affinity for protein phosphatase 2A (PP2A) as OA. NMR structural studies showed that DTX-1 possessed an equatorial 35-methyl group but that DTX-2 had an axial 35-methyl group. Molecular modeling studies indicated that an axial 35-methyl could exhibit unfavorable interactions in the PP2A binding site, and this has been proposed as the reason for the reduced toxicity of DTX-2. Statistical analyses of published data indicate that the affinity of PP2A for DTX-1 is 1.6-fold higher, and for DTX-2 is 2-fold lower, than for OA. We obtained X-ray crystal structures of DTX-1 and DTX-2 bound to PP2A. The crystal structures independently confirm the C-35 stereochemistries determined in the earlier NMR study. The structure for the DTX-1 complex was virtually identical to that of the OA-PP2A complex, except for the presence of the equatorial 35-methyl on the ligand. The favorable placement of the equatorial 35-methyl group of DTX-1 against the aromatic π-bonds of His191 may account for the increased affinity of PP2A toward DTX-1. In contrast, the axial 35-methyl of DTX-2 caused the side chain of His191 to rotate 140° so that it pointed toward the solvent, thereby opening one end of the hydrophobic binding cage. This rearrangement to accommodate the unfavorable interaction from the axial 35-methyl of DTX-2 reduces the binding energy and appears to be responsible for the reduced affinity of PP2A for DTX-2. These results highlight the potential of molecular modeling studies for understanding the relative toxicity of analogues once the binding site at the molecular target has been properly characterized.

year: 2009

title: Puhi: Memories and experiences in their ceremonial role in traditional and contemporary Maori worlds

authors: Simpson, Ariana

subjects: psychology

abstract: According to early writers, Puhi are described as the treasured daughters of chiefs, were of high rank, endowed with aristocracy, and fiercely protected and respected by the tribe. They were renowned for their beauty, their courage and leadership. Although very little information and knowledge on the function and the role of Puhi is available, information has been sought from early and contemporary writings, tribal narratives, oral histories and memories and experiences of women in their ceremonial role as puhi in traditional and contemporary times. Of interest for this research is the value and belief system in which the role and function of Puhi has survived and exists today, given that in today’s society, Maori women and their children are the primary victims of domestic violence in Aotearoa. This research aims to identify and highlight the importance of kotiro in traditional and contemporary times and to provide a clearer understanding of Puhi by documenting and recording experiences, memories and early writings.

text: Puhi: Memories and experiences in their ceremonial role in traditional and contemporary Maori worlds According to early writers, Puhi are described as the treasured daughters of chiefs, were of high rank, endowed with aristocracy, and fiercely protected and respected by the tribe. They were renowned for their beauty, their courage and leadership. Although very little information and knowledge on the function and the role of Puhi is available, information has been sought from early and contemporary writings, tribal narratives, oral histories and memories and experiences of women in their ceremonial role as puhi in traditional and contemporary times. Of interest for this research is the value and belief system in which the role and function of Puhi has survived and exists today, given that in today’s society, Maori women and their children are the primary victims of domestic violence in Aotearoa. This research aims to identify and highlight the importance of kotiro in traditional and contemporary times and to provide a clearer understanding of Puhi by documenting and recording experiences, memories and early writings.

year: 2006