Leading Edge Cell Culture: Oktoberfest At noon on September 18 th , 2010, the mayor of Munich will kick off Oktoberfest with the traditional ‘‘O’zaptf’’ as he taps the first keg of the festiv al. Over th e course of the next 2 weeks, more than si x million pe ople wil l celebra te the 200 th anni- ver sar y of Okto ber fest by sav ori ng roasted chi cken, jui cy wei sswurs t, and giant pretzels. But, mos t import ant ly, the re wil l be beer—enough beer to fill six Olympic-sized swimming pools. In this Cell Culture, we follow a typical beer at Oktober- fest, from its frothy pour into a 1 liter stein to its breakdown in the liver of an unseasoned tourist. Froth Factors Foam, fizz , fro th, or bubbles—the multi ple names giv en to the head of beer is a testimony to its upmost importance for beer lovers around the world. But why does this layer of foam form only in bee r and notothercarbo nated bev er age s, suc h as sod a andcham- pag ne?The secretliesatthebeer-bubble int er face,wherea pro tein in barl ey, the lipid -tran spor t protein (LTP1), prev ents the smal l bubb les from coales cing into bigg er, more fragil e ones. Now, according to Mills et al. (2009), a partial unfolding of LTP1 during the bre win g pro cess is key to stabilizi ng beer bubbl es and increasing the quality of the head. LT P1 is the pr imar y pr ot ei n in beer foam ( 40 mg/ ml) . Lik e det er- gents, LTP1 pos ses ses both hydro phobi c and hydro phili c surfaces, causing it to align at the air-water interface of bubbles, where it lowers the surface tension. However, unlike deter- gents, LTP1 molecules form an elastic network of proteins that can stretch. Thus, when the bubble starts to expand, the protein layer is held in place, pulls the bubble back into shape, and prevents rupturing. In other words, the protein makes the bubbles ‘‘sticky.’ ’ Most proteins in barley denature and precipitate when the barley and hops are boiled together for 1–2 hr before fermenta- tion. Us ing a combi nation of nuclear magnetic resonance spectrosco py and circular dicrohism, Mills and coll eagues find that LTP1 refolds after 2 hr of boiling. However, the refolding isn’t perfect, and a small segment of the protein at the C-terminal region stays unfolded. This stru ctur al rearrangeme nt enh ances LTP1’s surf ace pressure and localiza tion at theair-buffer inte r- face, improving its ability to stabilize bubbles. Thus, remarkably, brewing conditions have evolved to match the subtle biophysical properties of barley LTP1; the proper amount of boiling before fermentation maximizes the quality of foam by inducing a precise conformational change in LTP1. Mills et al. (2009). Biochemistry 48 , 12081–12088. Bitter Buds Of course, revelers at Oktoberfest don’t congregate in the ‘‘beer tents’’ to analyze foam, but rather to raise their steins, toast a hearty ‘‘Prost!’’ and savor the flavors of local Munich beers. Like most brews, the primary flavor of Oktoberfest beer derives from bitter compounds in hops. These mole- cules activate a family of G protein-coupled receptors, the TASTE 2 Recep- tors (TAS2R), expressed on taste buds of the tongue. Changing only a few amin o acids on a TAS2R rece ptor can dramatic ally alter an individual’s sensitivity to bitter compounds. A study by Hinrich et al. (2006) found that such small variations in TAS2R receptors influence not only individual pref- erences for ‘‘hoppy’ ’ beers but also the amount of alcohol one consumes on a regular basis (Hinrichs et al. 2006). A genome-wide sea rchfor genes tha t inc reasean indiv idu al’ s ris k foralco- holism identified a locus near a cluster of genes encoding the 25 human TAS2R receptors. Hinrichs et al. (2006) then genotyped four single-nucleo- tide polymorphisms within and flanking the TAS2R16 gene in 2310 individ- ual s (26 2 famili es) , app roximate ly half of whom were dia gnose d wit h alco hol- rela ted diso rder s. One allele within TAS2R16 was sign ifica ntly asso- ciate d with an incr ease d risk of alco holi sm. This substit ution (N1 72K) is located on an extracellular loop of the receptor that putatively binds ligands. Indeed, the authors find that the risk allele reduces the binding affinity of TAS2R16 for certain bitter compounds by 50% in vitro. Although future studies are needed to compa re the per cep tio n of bit ter tas tes among indivi dua ls exp ressin g thetwovariationsof TAS2R16, the seresult s sup por t thehypot hesis tha t enh anced sen sit ivi ty to bit ter compounds in bee r and oth er alc oholicdrinksmay reduce overall consump- tion of alcohol. Hinrich et al. (2006). Am. J. Hum. Genet. 78 ,103–111. The lipid trans port protein (LTP1) in barley stabil izes beer bubbles. Images courtesy of Alvimann (left) and A. Mackie (right). Hop flowers contain bitter compounds that acti- vate TAS2R receptors. This photo is licensed from F li ck r user dun ca nh1 ( http://www.flickr.com/ photos/duncanh1/ ) under a Creati ve Commons Attribution license. Cell 142, September 17, 2010 ª2010 Elsevier Inc. 827