UPDATE 4-Pfizer acquires rights to Protalix's Gaucher drug

* Buys rights for $60 mln upfront payment

* Protalix eligible to milestone payments of up to $55 mln

* Protalix to retain marketing rights to drug in Israel

* Protalix shares fall as much as 15 percent (Adds Pfizer, Protalix comments)

By Esha Dey

BANGALORE, Dec 1 (Reuters) - Pfizer Inc (PFE.N: Quote, Profile, Research) said it would acquire worldwide rights to Protalix BioTherapeutics Inc's (PLX.A: Quote, Profile, Research) experimental Gaucher disease drug, Uplyso, for an upfront payment of $60 million, disappointing investors who were expecting the Israeli biotech company to be acquired.

Protalix shares fell as much as 15 percent to $8.41 on the American Stock Exchange, while Pfizer shares were up 3 percent at $18.73 on the New York Stock Exchange.

"There is some immediate-term disappointment that Protalix wasn't outright acquired, but I don't think this precludes the potential for them to be acquired down the line," Oppenheimer and Co analyst Brian Abrahams said, mentioning Teva Pharmaceutical Industries Ltd (TEVA.TA: Quote, Profile, Research) (TEVA.O: Quote, Profile, Research) and Pfizer as potential buyers.

However, analysts said the deal is a validation of Protalix's drug technology and would eventually boost the company's value.