K. SAEKI (1), A. Suyama (2), K. Takegawa (2), M. Sato (1), T. Shigyo
(1); (1) Sapporo Breweries Ltd., Shizuoka, Japan; (2) Kyushu University,
Fukuoka, Japan
Analytical
Friday, June 6 - 2:00 p.m.-3:45 p.m.
Level 4, Red Lacquer Ballroom
Foam is one of the most important properties of beer. Many factors,
including barley and hop varieties, malting conditions, and yeast
strain, influence foam production and stability. There are also factors
that negatively affect foam quality, such as lipids, alcohol, and
proteases produced by yeast. Yeast-derived vacuolar protease proteinase A
(PrA) digests proteins in beer and, thus, impairs foam stability.
“Vacuolar” protein PrA is normally transferred to vacuoles from the
Golgi, but under specific conditions during fermentation, PrA leaves the
cell for some reason, which is detrimental to the final product. In the
brewing industry, PrA has been of great interest for more than 40
years. Methods of measuring PrA activity in beer have been established,
and several trials have been performed to reduce the amount of PrA
excreted in beer. However, the fundamental mechanism causing PrA to
leave the cell has yet to be elucidated. Therefore, we conducted assays
to monitor the behavior of PrA and its related proteins both inside and
outside of the cell, aiming to identify their relationships in the
intracellular transport system. PrA is mainly transported to vacuoles
via Vps10p, a vacuolar protein receptor located in late Golgi. Vps10p is
also involved in the transport of another vacuolar protease,
carboxypeptidase Y (CPY), so we hypothesized that the change in the
ratio of these three proteins would be crucial for the irregular sorting
of PrA toward the outside of the cell. To demonstrate this, we
performed western analysis and protein activity assay to analyze the
amount of each protein both inside and outside the cell. Fermentation
tests were also conducted using various kinds of wort with different
compositions to reveal its effect on PrA activity in beer. Analysis with
yeast in shaking culture indicated that different growth conditions
cause changes in the amount and activity of each protein and that they
also affect the ratio of these three proteins. Based on these results,
we proposed a model to describe how PrA leaves the cell.
Kei Saeki received a master’s degree from the Department of
Biotechnology, University of Tokyo, Japan. She began her career as a
microbiologist in 2012 at the Frontier Laboratories of Value Creation,
Sapporo Breweries Ltd. In 2013, she started her studies in intracellular
transport supervised by Professor Takegawa at the Department of
Bioscience and Biotechnology, Kyushu University, Japan.
