** Shares of Protagonist Therapeutics PTGX.O rise 28.3% to an all-time high of $86
** Johnson & Johnson JNJ.N is in discussions to buy PTGX, the Wall Street Journal reports, citing people familiar with the matter
** A deal is not guaranteed and the exact details being discussed could not be learned - WSJ
** PTGX has a market value of $4.17 billion as of last close - LSEG data
** Up to last close, stock up 71.4% YTD
(Reporting by Puyaan Singh)
((Puyaan.Singh@thomsonreuters.com;))