In pre-war times, the Sukhoi OKB was based at Zavod No.135 in Kharkov, Ukraine. Therefore a fighter designed here was designated "Zavod 135 fighter" - I-135. In the same way many other contemporary aircraft were designated: Lavochkin/Gorbunov/Gudkov I-301 (which became LaGG-1 and then LaGG-3), Pashinin I-21 (or IP-21), Borovkov/Florov I-207, etc. In December 1940, when the new designation system was inserted, the I-135 became Sukhoi Su-1.
The often mentioned designation "I-330" is probably incorrect: "330" was only the purchase order number.